1970 DUSTER WITH DISC BRAKE CONVERSION WHEEL HELP
OH NO SORRY, THATS TERRIBLE
Agreed...so maybe no follow those tire recommendations. :D
Your original idea of 15x7s up front is FINE. If you were going for a factory restoration, you wouldn't be considering disks anyway...so at least go for the wider wheel. With that size you can fit a 225/60/15...guys do fit 275s on the back and it is possible without mods but its tight without a spring relocation kit which you may or may not want to get into. You also may need a small spacer and rolling the fender lip...again which you may not want to get into.
I have 255s on my 15x8s on the back of the Dart Sport and they look fine...and they're already a bit too wide for 8" wheels (which need 9" wide rim to be optimal). Probably no benefit to going wider with a street tire on those wheels anyway.
Keep in mind that any tires available in 15" size, not counting drag tires, will be all season tires and absolute JUNK by modern standards. So drive carefully.