The sidewalls will pucker in, but they will mount. I have a set of Khumo 315/35/17 on 89 rims and run them in the autocross with no problems. They just look a bit strange and I don't believe you get the full contact patch. 11 inch is definalely the way to go if you can swing it.
I had 315 Eagles on my '93 Sawblade (9.5") wheels and I had worse traction than with my 16" stock 255's..
Of course I dont haev that issue (too much) anymore.
You will loose "some" footprint if mounted on 9.5" rims, but it can safely be done (as most drag racers here are doing). You just don't get the best use of that size tire on that rim, but if you can't afford, or just flat out don't want to buy the 11" rims, go ahead.
Anyone have a pic of a BFG DR 315/35/17 on a stock (such as a 17" Z06) rim? Was thinking of going with the combo vs. the 275/40/17, traction is my biggest concern.