Greg
I am sorry I have taken a long time to reply but I have now measured a clutch throw out bearing offset on an AC Saloon clutch which should be similar to the CLB Aceca engine, the distance from the centre of the journal which fits into the yoke to the carbon face is 1.148" , this is a used carbon but looks fairly unworn so it is probably 1.150" or thereabouts!
If you contact the Austin Healey BN1/2 parts suppliers they should have a similar carbon thrust assembly, so should be able to find one in USA, if not try AHead4Healeys in the UK.
Regards
Robin