would a later ZX brake booster work or should i say fit. and would it be worth it to upgrade to that booster and master cylinder or just get the stock booster replaced with the later ZX master cylinder

Not sure if the whole booster assembly will work or not. I'm willing to bet not many people have tried it since all they have to do is use the later 15/16 master on the one they have. If the booster you have is OK then I'd save the money for now and just go with the master swap.