different thermo quad bodies

I've got two different phenolic bodies off of the two TQ's I have. one is off a 76 400 lean burn and the other a 77 400 hp. The first picture shows a port on the 77 400 carb that the 76 doesnt have. BUT the 76 was a reman'd carb so I can't guarantee thats the right phenolic body. Its a lean burn motor that I'm converting. I need the 77's base for the ported vacuum. now I'm wondering if I'd be better off w/ its body as well. The one on the left is the 77. also theres a port between two holes in the front as seen that the one on the right doesnt have. Whats this vacuum port for, and the other groove as well?



also on the 76 reman'd carb body theres two grooves this plate can hang in. the 77 only has the one in the position the plate is in. The one it doesn't have is the one being pointed at in this picture of the 76's body. what would be the reason for positioning it in the other slot? Is it for gas mileage?



So which body do I want to use and why? Thanks for your time on this guys, I know nothing of TQ's yet but I'm learning.