I put Wheel Vintiques “Chrome Hot Rod Rallye wheels on my ’63. Not sure about what offset they are. They are 14″ x 6” with P215/70R14 BF Goodrich Radial T/A’s in back and P195/70R14 in front. The slightly taller and wider rear tires give the car a slight rake. See photo. There is about a finger’s width between the tire and the wheel opening trim on the rears. I wouldn’t go any bigger than this unless you plan on tubbing the wheel-wells. I haven’t had any interference with any rubbing. You might do some research on what the offset is on these wheels and use that info. to find wheels you like.
I scored a set of used aluminum slot mags from a 1960s Mustang with the six cylinder motor. The bolt pattern is the same 4 x 4.5″. Note that the Fox-body Mustangs with four bolts do NOT use this same bolt pattern, only the 1960s six cylinder cars (as well as Falcons and Comets from teh same vintage). The wheels are 14×6, with about zero offset. I’ve got 195/70-14s front and 205/70-14s rear.