Ken Breslauer's book - Sebring - lists the cars as:

#23 Austin Healey 100/6 2680cc - Phil Stiles/John Bentley  - entered by Hambro

#24 Austin Healey 100/6 2680cc - Roy Jackson-Moore/E Forbes-Robinson - entered by Hambro

#25 Austin Healey Special 2680cc - Gill Geitner/Ray Cuomo - entered by Hambro
 
Far from being the poor relation of the Healey family, the 100-Six has the most varied and interesting history of any single model type. The Streamliners confirm this. They must be the most exotic of all Austin Healeys, and the rarest.....as it appears that none now exist!
    
Were the Streamliners real 100-Sixs?

The two pictures below compare the 1956 endurance car with one of the 1957 Streamliners. The point of comparison is the place where the extra 2" of the 100-Six chassis should be  noticeable. They are not quite at the same angle and it is difficult to be certain  whether the door on the 57 Streamliner is larger than the 56 car. It is also possible that that one car may be a 100 and the others 100-Sixs. .
 
The Streamliners
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'56 Endurance Car
from many sources including

The Story of the Big Healeys
Geoff Healey

The Healey Book
Bill Emerson

Sebring
Ken Breslauer

Healey, The Hansome Brute

Austin Healey 100 & 3000

Graham Robson

The Works Big Healeys
Peter Browning

Works Wonders
Marcus Chambers

www.
racingsportscars.com
 
 
Three 100-Six Streamliners on the grid at the 1957Sebring12  hour race

source
www.
racingsportscars.
com
Ray Cuomo
Car # 25 landing after striking a kerb due to being forced off line. The car made it back to the pits where temporary repairs were carried out. Cuomo finished the race in 26th place
Car # 25

According to Breslauer's book this car was listed as a Special, but what was special about it?

The accepted opinion is that it is probably the car that was fitted with a
Ferrari 2 1/2 litre Grand Prix engine. The DHMC purchased a Ferrari GP car and fitted the engine and transaxle gearbox to a 100S chassis. Geoff Healey refers to this car in his book "The Specials", and it is referred to as X224

Geoff Healey also mentions that one of the long nosed 100-Six Sebring cars "was cut about and  the Ferrari de Dion rear axle cum axle was fitted." It is not exactly clear if he means it was fitted before or after Sebring. 
Research on the Streamliners contributed by

Patton Dickson
Peter Dzwig
Philippe Dubois
Ken Freese
Derek Job
Patrick Quinn
Keith Turk
Rick Wilkins
  
home
Sebring 1957

 
 
Donald Healey with the 1956 Endurance car outside the Cape Works in Warwick.

The white inlays must have been added after this picture was taken.

The Healey in the background is Patrick Quinn's BN3
  
Geoff Healey mentions that Jensens also fabricated three other aluminium alloy bodies for racing purposes and it would seem that these were installed on the cars shown below, on the grid at the 1957 Sebring 12 hours. These are the real 100-Six Streamliners.

There are conflicting descriptions of these cars and it is still unclear if they are 100-Sixs and not special bodied 100s as was the 1956 endurance car. They are described by one source, (www.racingsportcars.com) as 100s and  that car# 23 is AHS 3804. This is surely not the case as that is Fred Hunter's car and there is no evidence that it was ever bodied in this fashion.


Breslauer's information is partially incorrect as Marcus Chambers says the cars were 2639cc which is more logical as that was the standard capacity. He also mentions the cars had nitrided crankshafts and were good for 150 bhp at 5000 rpm.

Only one of the cars finished the race, the other two retired with cracked connecting rods. This was established when the engines were stripped by Eddie Maher back at the factory in the UK. The result of these findings was redesigned connecting rods for production cars, which never gave any further trouble even  in the uprated engines developed for racing and rallying.
100-Six
next
 
 67yu
 
  
'57 Streamliner - (mirror image)
  
1956 Endurance Record car

- 6-port head
- triple Webers
- 10.2:1 compression
- 156 bhp
When taken together with the other evidence and the fact that in 1957 the 100-Six was in production I think its possible that one or more of the Streamliners were real 100-Sixs.  Would they have rebodied two more 100s at that time? That may not have made sense from a marketing viewpoint when the objective was to promote 100-Sixs

If we accept this as fact then the next step is now to find out  their chassis numbers!!.
  
  
The above picture shows Stirling Moss driving the 1956 Endurance car at Nassau Speed Week in 1956 (nice to know Stirling Moss drove a 100-Six!). It appears that he may have been just testing the car or driving in a minor event  as he is not listed as driving the Healey in either the Governor`s Race or the Nassau Trophy, the latter of which he won driving a Maserati 300S.

The above car was driven by Shelby, Jackson-Moore and Donald Healey at Bonneville in 1956 when the car  set many International Class D endurance records. (The car was  Healey Blue and White in colour) The record setting was used to promote the new 100-Six introduced later in that same year.

This streamlined car was the same car
(SPL 227B) as that used in the record setting in 1953 and 1954 and is based on a 100 chassis. However the 1956 version had a six cylinder C series engine of the type later introduced in the production 100-Six although with appropriate modifications, which included triple Weber 40 DCOE's and a 10.2:1 compression ratio. The other key difference was that it had a specially designed streamlined aluminium body made up by Jensen under the guidance of Dr.John Wevering. This was the first appearance of the Streamliner.
  
The photo on the left shows the X224 Streamliner at the Nassau  Speedweek in  1958. The car was driven by Roy Salvadori who is pictured standing behind the car with his hand in his pocket. Roger Menadue is attending to the front wheel.
The following is a summary of information taken from an article written by Joe Jarick (Brisbane, Australia), which was published in the May 2006 of Healey Marque.

According to Joe the inaugural outing for the Ferrari engined car was the
1957 Nassau Speed Week, which would mean it did not run with this engine at Sebring in 1957. The car was driven by Peter Collins, a works Ferrari Grand Prix driver at the time. The donor car was purchased from the Marquis de Portago who was tragically killed the same year, at the 1957 Mille Miglia. The car had a 2.5 litre 4 cylinder engine which was tuned to run on methanol. This had to be modified to run on petrol for the Nassau event and as a result there was a drop in horsepower from 240 to 210bhp.  The car was a bit of a disappoitment, finishing 10th overall and suffering from very high oil consumption.

During early 1958 the Ferrari engine, transaxle and rear end were removed from the car and X224 was rebuilt using a six cylinder Austin engine and transmission. The car had about 175 mph but was better sorted than with the Ferrari engine. Salvadori finished second in one of the main races but retired in the second due to clutch problems.