15x8 with 4-1/2 backspacing fits with no rubbing. You might fit a 15x9 with 4-3/4 BS but it would be real close to the inner fender. 255/60-15 will fit either wheel. Maybe you can get a 275 in there, but it would be real close on both sides. 255 is more than enough tire anyway.
It looks like there's all kinds of clearance there, but the outer wheelhouse slopes a bit near the lip, so if you want to be safe, go 15x8 and 255/60.
_________________________
1988 CVLX Formal Roof (Love Boat)
POTM July '19, Aug '20, Oct '21, Feb '23, 64K
E-code lights w/ relays, LEDs w/ switchbacks, 15x8 Ansen slots w/ 255/60 BFG's, Kenwood stereo, various hacks.
This, of course, was merely the semi-delirious notion of a fever-patient, but I remember that it struck me at the time as being eminently practical and feasible.