There's supposed to be a black little plastic hose sticking out by where the heater hoses go through the firewall. That line runs to a 3 port check valve. The side on the same side as that little black line goes to a vacuum reserve ball behind the passenger fender. The other side of that check valve runs to that AC spot on the vacuum tree.
See pictures below....
The AC line from the tree traces along the firewall behind the upper intake and connects to a plastic check valve as Described in the above post. I hope these pictures help.
im trying to delete smog first I ran shorter belt but now it's squeaking from the idle pulley from time to time and it's brand new I'm looking for the idle pulley so I can run the stock belt and I put a cap on the smog tube but how do I cap the hole in the h pipe someone said make it flat and JB weld it but it's on the car still thank you again here's my 91 gt and it took me forever with a new distributor to set it