How big can I get under this with out cutting it up. 325 or so? Rearend width can change
Up front, it depends on how much backspacing with what diameter rim you can use on a Reily front end.
I could barely fit a 245/50/15 tire with 15x8 rims 4.5" backspace on my 68 Barracuda with stock front fenders. Those are 27.8" diameter. Equal in diameter to a 245/40/17.
IIRC, the RMS front end moves the rotor face outward. So you have to ask Bill how much more outward it is from a 1973-76 big bolt pattern disk brake setup (what I had).
My pure guess is you'll need something around a 6.0" backspace 17x8" rim with 245/40/17 tire. Just an initial guess. You need to get spec from Bill.
In the rear, is it allready minitubbed? Are you againsted mini tubbing it?
In the rear without touching anything you can fit a 275 back there.
