As I recall, there was something different with the Polys supplied to Bristol...
I don't remember the details now, but it was a performance enhancer of some kind. As they were 318s from Canada, where they only made 313s, maybe that was it, or maybe they had higher compression ratios, I once found this detail on the net somewhere. The next model, the 410 (pictured), was very similar and was the car used in the 'Inspector Linley Mysteries', a British detective show made between 2001 and 2008.
Still bouncing thoughts around in my mind, I wonder if that difference I was semi-recalling was that they retained the older-style (pre-727) Torqueflite well into the sixties? Not a performance thing at all and requiring a different crankshaft.
Something was different, anyway, maybe our new member can tell us.
I only ever drove one Bristol, a 403 owned by a friend, it was the later one with the Borg-Warner gearbox and, of course, it had the Bristol 2-litre engine which was copied from the BMW 328, a design taken from the Germans as war reparations. Single cam in block, one pushrod for the inlet valves, two and an extra rocker for the exhausts (as I recall). It was a lovely car with an alloy body.
Anyway, welcome to the new member, that's certainly something different.