I didn't adapt one, I used a Vintage Air system that was (supposedely) engineered to fit. It clears the battery box nicely, lines exit sheet metal below battery, one screw goes thru firewall to hold evaporator case in position. (1959 1/2 ton)

If you want to try and adapt one, try to get one from a smaller import car, they are usually self contained under the dash and small enough to fit behind the dash. Not a whole lot of room there.