I am finally thinking hard about putting a new AC system in my 76-L48 (equipped with factory air).  It has never worked since I got the car although the compressor switches on and off once I fixed some wiring problems.  I suspect to do a conversion to R134 and fixing other possible problems might set me back close to the same price as a replacement system and, if not, probably wouldn't work that well anyway - so kind of leaning toward a new system (can't stand the hot summers any more even with the tops off).  I'm not that concerned with keeping this part of the car stock - although most of the rest of the car is (76 non bumper, just not the valuable in stock form).

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. 

I have the vintage air in mine....I didn't put it in and the system is not designed for a vette..didn't have them at the time..I got to say though..they do now make a system for the vette..and have had one minor problem with it since I got the car...the people at vintage air were awesome..I even met up with them at their vendor booth at the York hot rod show un announced and they had the part I needed with them and gave it to me for free..which it was only a 5$ part anyhow but still made an impression..this is a 11 year old system and they still had parts for it..plus it does freeze the heck out of me when I do use it...which is rare since the top is rarely up...and that's the only time it really works anyhow..the only thing that I would see you using a shop for is charging the system..running a vacuum down and removing all the air is key..plus not over or undercharging the system..have fun!! Rich

If You're still thinking about Vintage Air I'd say go for it. My car was non a/c it took me a while to get up nerve enough to start but after going over directions a few times dove in. Everything went well, one time called customer service because harness had extra wire and they were very helpful. Liked the way it was packed each box had it's own directions. Was worried about dial controls but all went fine.  Cools really great would do it again.
Ray

There's also Classic Auto Air if you are still looking.

Thanks to all for your replies.  I checked both sources and their prices are similar.  I am leaning toward Vintage Air, assuming I bite the bullet.  I am working on a truck too, so have to carve out the time and cash (want to stay cool though and  the vette is cheaper to drive).