Thanks for the great input guys!
The situation has changed as I may have run into a set of Keystone Klassics that were on a '68 GTX. I think I might go with this set up: Fronts are 15x6, 215/70R-15 and the rears are 15x8, 275/60R-15. I might be able to get the whole deal for $250. This might be a nice way to go, sort of period correct. Plus the price is decent and supposedly they look like they're in nice shape. I'll check them out tomorrow. I think the max on the back spacing is 4 to 4.5 inches. I figure if they were on a GTX it "should " work, I think. Thanks guys! I'll fill you in tommorow.