The differential is stamped on the upper side of the nose casting. It's only stamped with a makers number and another code prefixed ACH and the ratio 12/47 or 14/51 ect, not with anything that was chassis specific.
The Aceca Moss gearbox I have has no stamps, I don't have a Bristol gearbox at present but I think they are also only marked with their type such as BWCR9, but I guess they could have been matched to a specific engine block, maybe someone else will know for sure.
Regards Luke.