Which Brake Booster??? Help!!

Actually at least the earlier cars used a 1" MC on both manual & disc A-body apps. I used a 1" for mine & it works fine, good feel & stops strong, Wilwood calipers. I'm sure 15/16" would be great as well. I'd be inclined to go with a later aluminum if you don't care about the appearance of the era, the iron original replacements are all Chinese or sketchy rebuilt, I had a heck of a time getting one to work for any period of time & ultimately had to rebuild one myself.