275 will fit with only slight hammering and i think at least a quad shock flip. My buddy has 295s on his coupe with a little help from a sledge, no quads and eibach drags
275/60's are too tall in my opinion. I had them on my 91 GT and they looked way too tall. I replaced them w/ some 275/50's and they look way better. They fit the GT w/o any spacers or flipping the quad shocks, however I did have to massage some of the inner-fender areas. I just put them on my LX yesterday and had to use 1/4" spacers and beat in the quad shock a little bit (didn't wanna flip it). I think they look better on the LX than the GT because you can see more of them w/ the LX rear bumper than w/ the GT rear bumper.
I have pics of the 275/60's and 275/50's on the GT if you want...