I am running OE Wheels ZR1 17x9 front with a 275/40/17 and 17x11 rear with a 315/35/17 rear. Koni yellow sport shocks with Hotchkis springs. SLP rear axle bump spacers with urethane bump stops.
I ran the same size on my hardtop and it would rub in the rear when loaded down on Hot Rod Power Tour. But only on bad dips especially at highway bridges. I did not roll my fenders though which I might do a little on the convertible. I did do the heater hose wrap on the springs and that helped a lot too.
Since you have a 255 front and rear I don't see where you would have a problem? Not even with a 275 since was an optional factory size.