BOLT IN REAR SUSPENSION ?

I have a 68 Barracuda, and the tubs will physically accept a 325/50-15 on a 10" rim, between the inner wall and the outter. I did have to pound the inner wall in a few places, and I did have to fold a small portion of the fender lip,
for clearance, to corner more than idling around,and I did have to offset the springs.

However 295/50-15s on 10s fit just fine before the fitting of the 325s, and I drove the chip out of it with no rubbing.

So 275s are not a problem to physically fit into your tubs. And the springs do not have to be moved. But the backspace on the 9.5s will need to be just right so that she don't rub. With a zero-offset 9.5 wheel, the backspace should be about 5.25. That's fine but I think the springs, without offsetting, will likely get into the sidewalls. So
you will probably need to run long studs and spacers to push the wheel towards the outboard side, to get it off the springs.

IMO, offsetting the springs is not a big deal, unless you are in some way physically handicapped.

I ran 275/50-15s and 275/60-15s on 8.5" rims right in the un-molested tubs and springs on zero-offset wheels. That would be a 4.75" backspace.