275/60/15 woes

I couldn't agree with slantsix64 more. I love wheels with too much backspace, that can be fixed/adjusted with spacers. Too little, the tire crashes into the fender. As he pointed out, you already have the necessary studs. No brainer in my opinion!
Next, I think the reason that it didn't work, going in, is cause of the narrow brakes on a sbp 8 3/4, the wheel mounting face-spring distance is a little shorter than the average
8 3/4.