Whats a nice sized tire for a fastback Cuda

i am running 255/60 15 on a 7" rim 4.5 inch backspace. I have +/- an inch to the inner spring. it fits well with no rubbing and fills the rear fenderwell good with stock profile.
best to take all measurements and find what will best fit your car as things change a bit after 45 years. such as was the car ever hit etc...