I have used Tim Tygart's Obsolete Chevrolet Parts in Nashville,Ga with great luck. One big plus is the fact that I get most orders in two days, sometimes the next day because they are so close. Quality has been good but admitadly most of my orders thus far have been sheet metal items.
http://www.obschevy.com/

1947, 1950, & 1952 Chevrolet 1/2 ton
1952 GMC 450 series Cab Over Engine
1946 Chevrolet 2 Ton