What size plug is needed to plug ac at firewall?

What size plug is needed to plug ac at firewall?

ttt

I am not sure anyone knows what you mean (could be why you are not getting any response). Maybe you need to add some info. It's definitely not an LT1 engine tech forum question.

You talking about the big square hole after you remove the ac/heater box from the firewall? There is a company who makes a premade piece for that or get a piece of sheet metal or aluminum.

Or maybe the two threaded holes left in the evaporator, after you remove the tubing?????