I presently have 275/60-15 Nitto Drag Radials on 15 x 8 rims on my 68 Barracuda with stock wheelwells. If you get the backspacing just right they should fit without an issue.
Agreed.
For the street I run M/T ET Street 275/60/15s on 8.5" Centerline Prostocks with 4 7/8" backspace and std tubs.
I do however have SS sprigs which raise the rear some and make fitment easier.