I bought my system from Nostalgic Air Parts. I too had AC to my car already so I just used the system without an evaporator.
If you need to replace your evaporator then I would go with one for the 78-79. It will bolt in and you will not have to deal with the VIR valve.
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Brian - NCM Lifetime Member
73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System
Dewitt radiator and dual electric fans
Borgeson Steering box