Reid--
This matter is covered in your recent "Healey Marque" article on the 1957 Sebring cars.
Aside from Phil Stiles another person that might have been able to provide an answer to the question was Ed Bussey of Ship and Shore Motors in West Palm, Florida, a BMC importer/dealer. Partly at your behest I interviewed him in January, 2004 and perhaps you may remember an article I wrote for the February Capital Area AHC newsletter which may be found at:
https://www.capitalhealeys.org/Assets/Miscellaneous/HHR pdfs/hhr_feb_04.pdf
It is a shame I was not armed with questions about the issue when I sat with Bussey. At the time it appeared to me that Bussey's health and memory were declining and though he was vague on some matters it was clear that he had a wealth of information available in his memory. He also had much paper documentation coming out of his business and I got the distinct feeling that it was destined for a shredder after he passed.
Since the wheelbase of a 100-6 is longer than that of either a BN1 or a 100S perhaps by measuring or in some way scaling the wheelbases of the cars pictured we could get an answer to the question. I know we have only old photos to go on and the cars are shot at angles but maybe points of reference could be established in enlargements, etc.
At a time when the most minute details of so much is instantly available to us it is nevertheless true that so many facts and so much knowledge has simply fallen into the ashcan of history.