Hi again Stephen,
Both the 376/6 and 376/16 have 1 inch bores so should work ok with your 15/16 inlet manifold as long as it's not too badly worn and that you don't intend to thrash your engine. Make sure that the flange is flat where it mates up to the inlet manifold.
The 376/16 was fitted to the 1955 BSA A7SS so I reckon that this would be a good base to start. Originally it was set with the following:- 270 main jet, 30 pilot jet, 3 1/2 cutaway slide, .106 needle jet and the needle on number 3 position. I would use these settings to start with and then modify slightly if any fine tuning is required.
During the experimental stages a slightly rich mixture will be better than a slightly weak one. It's always a little "hit or miss" when using a carb that wasn't made for the job but I'm sure that you will be able to sort it out.
Beezageezauk.