With the roadkillcustoms link above, I can verify that the dummy spare tire from the 2005-2008 Chevy Cobalt fits my 1970 GT front and rear with no clearance issues. Bought my car and it had 4 dry rotted and and/or flat tires on it, and since I've got a lot of work to do to it and need to be able to roll it around, I didn't want to buy new tires for the 13" wheels that are on it because I don't know, but might be going 15" in the future. I went to the local pick n pull yard and found 4 dummy spares off the Cobalt and they fit fine. The hub center bore cleared just fine. Had to get some taper seat lug nuts from Napa, but the wheels work well enough to be able to roll the car around on.
Don't know if the regular wheels fit very well, but the dummy spares work for what I need them for.