Juan, the community would be grateful if you identify that compressor for us, please?
The compressor is no big secret, I have been using a unit from a Suzuki SX4; which is made to cool a small SUV. I made the brackets for a GT and also two different style pulleys, so it could be used in a V-belt or 5 rib serpentine system. It is very efficient when the components are match to the system.
And if it is THAT much better then Keith will probably have to redesign his compressor bracket to accommodate it.
Harold
I believe Keith is doing fine on its own. If anything I would offer to make the brackets for him so at least he would have a fair cost.
Perhaps I'm oversimplifying things but couldn't the "venting" be accomplished by adding the cooling side of the AC coils to the "cold" (or rather recirculating) side of the heater assembly?
Then a simple AC ON/OFF switch to go from recirculating to AC. You could even engage the AC during the defrost, for those who are still crazy enough to drive a GT in the Winter.
I know I have said this before but on a GT, the first thing that is needed when adding A/C is to seal off the two side vents. You then have to seal the main outside vent that is over the heater/blower core as well. To do this properly, you would need to take the dash out, perform the work and then re-install it. If you don't, you loose about 30% efficiency due to the outside air being injected and might not be cold enough for some places.
There is no way to modify the existing heater/blower system to add A/C. The room available inside the case does not allow you to do it, and that is why the bulky console with the rear evaporator was added. Several years ago we made a heat/cool unit for the GT and other small cars with limited depth in the passenger side dash area. We offered it for sale to Opel owners, I even offered to install one free of charge and document how it was done, no one wanted it. So we changed the design and sold plenty of them to other car club members. I still have the molds to make the case, tooling for the flanges to mount the blower motor and so on, inside a box stored at Radical rides.