Hi Andrew,
I came across this firm yesterday afternoon who may be able to help, I rang them this morning on the second number and while not certain of the type of joint fitted to the Bristols the very helpful chap said that if you can give them the dimensions , number of serrations in the joint and a photograph they may be able to supply a suitable replacement, an example he referred to was 3/4" 48 serrations. Do let us know how you get on.
Geoff.
https://steering-racks.co.uk/location/