I'm using '81's on my '77.
Single petcock and Uni pods. Had to trim the side cover tins a bit to fit the different length in the carb bodies, if you use the tins you'll see what I mean and what needs to be trimmed. Of course use the '80 intake manifolds. Cap the vacuum tits on the intakes or loop them together with some vacuum line. The stock manual petcock from the '77 tank should be fine.