68 Barracuda. How Big Can I Go? Rim and Tire?

loganscuda said
275/50/17 nito rear
215/50/17 front coopers

Are the rear fender lips rolled?

On my 68, I got 245/50/15 on 15x8 with 4.5 backspacing with small bolt axles (re-drilled lbp) on stock 40 year 340 leaf springs. No lip rollig or trimming.