15 x 8 Americans

I know alot has been posted as to what will fit on 67 to 69 fish's, American racing has Outlaw 1, 15x8 rim with a 3.75 rear spacing ( large bolt pattern ). Thats all the catalog lists. I will change my rear axles for the lg bolt pattern and as I have 14" outlaw 1's on the front now. Anybody see a problem with 255's or 275's with this rim? I will have either SS springs or Caltracs on it so I would hope if the tire sits out a little it would be alright. Thanks Kevin