Yup, 1973 is the 1st year Air was available in ANY Z28, due to the non-solid lifters among other things. Plus, a 4 speed Z28 with air forced the wide ratio M20 as opposed to the M21 close ratio trans.
Finally, you can't (easily) swap A/C from an ac car to a non-ac car. Unless you punch open the firewall and substatially change the under dash ducting, venting, wiring, the dash itself.....
Sounds like the dude got caught on the A/C issue already. I'll bet the car also has the "rare" trim tag that doesn't say Z28 on it - like (almost) all the real ones.
That's tough - it could be legit (because the original engine is apparently still there).
[This message has been edited by NastyZ (edited 09-27-2001).]