For street driving, and transforming a Pro/Street car to the more modern Pro-touring style ...
You may consider 18" wheels up front & 20" in the rear.
For front tires I'd suggest you go as wide as will fit. Get creative with back spacing, inner fenders & actual needed turning radius & you may be able to fit 275+. Remember, the front tires will be the key to cornering, and the bigger the difference in front & rear tires, the more of a push condition the car will suffer from.
For rear tires, Mickey Thompson makes a new line of short sidewall radial tires for street driving. Check them out
here.
I don't think you have to completely fill the fender opening or the tub width to look right. But, you need bigger than most.
M/T's #6620, the 29X15.00R20 equates approximately to a 365/30R/20. If you decide to go narrower, there are several good brands of tires in the 285-335 width range.