Need advice on tire/rim size for my 69 cuda

The rear wheel wells on the 2nd gen Barracuda's will allow for some good sized rubber in there. I am running 15" x 7", with 4.25" backspacing, steelies all the way around. IMO, plenty of rim for you needs. Runnng 215/70/15's up front, and 275/60/15's out back. Stock front suspension rebuild, and SS springs out back, with the addition of 1/2" spacers to get the tires away from the springs.