front wheel size for 1968 Dart

You didn't say if you had shortened the axle housing, but you shortened the axles? Stock housing will take 15x8 and 4.5 backspace. 255/60x15 tires. With a 4.75 backspace, you might get 275's in there, I think they would fit my '69 anyway.
I have more room on the inside than outside with 255's and a 4.5 backset.