275/60/15 woes
Move the springs; you won't regret it; I have fit 325/50-15s, on 10s, into the tubs of my 68 Barracuda, which is lowered. Yeah, I had to massage the inner metal a bit, but I did not roll the lips, just bent them up in one spot on each side.
I'm pretty sure the Barracudas and Duster/Demons share the same inner tubs.