Tire size question

275/60-15s calculate out to 27.99. Installed on 8.5s they might be a little under that.
295/50-15s calc out to 26.61. Installed on 10s, they are closer to 27
That is a 5% difference., with a ride height drop of about .7 inch
28s are about the max you can fit,if you can keep the tire in the tub. As soon as it moves out a bit, it is in danger of rubbing on the outer fender,bottom front corner. I moved my rear-end back a half inch for clearance, to fit those.
The -5% is about one gear size, making 3.55s a blast.
3.25/50 15s fit in my stock 68 Barracuda tubs.They calc out to27.8 tall. With your bigger tubs, these should slide right in there. Mine are on 10s, but it wouldn't hurt for the rims to be wider. I cannot run more than 24psi, to get even treadwear.Ima thinking 12s. I cannot run more than 10s cuz the section width would grow,right into, everything.