What rim size can I run?

Not sure on the Val, but on my buddies 70 Dart we are running 255/60/15 on 8in rims. On my 72 duster I’m looking at 275’s on a 10” rim... best would be to take to a custom rim / quality tire shop and have them measure your wheelwells and go from there. Summit has repop rallies for big and small bolt pattern...