Yes, that's a mismatched set, one '78-'79 and one '76-'77. The earlier carb can't be any older than '76 because those didn't have the casting on the bottom to mount that angle bracket to. They will probably work like that as long as the slides, needles, and needle jets are matched. A small issue will probably be mix screw settings. They won't match carb to carb. The '78-'79 carb calls for a setting of 2.25 turns out, the '76-'77 carb is 1.5 turns out.