need more tire somehow

72 dart 440, Got small bolt ralleys on it with 235/60/14 tires on the rear and they are too small..need more tire under there. From reading around on this site, it looks like i could get a 255/60/14 under there but i cant find that size in a 14 "..I thought about ordering a small bolt 15" ralley from wheel vintiques or something but not sure on the backspacing and all.. any ideas?

I was able to fit 255/60/15's in the back of my 68 fastback.
Those Duster guys are better off.