A few years ago, I was able to get a 245/60/15 street tire on a '65 Valiant with no modifications to the wheel wells or spring location. I put new leaf springs in though and had them arched 2" over stock to get clearance. They settled some and looked OK. I used a 15 x 8 wheel with 4.875" backspace. No rubbing at all.

You could possibly get it done with the offset spring hanger but a mini tub would probably be best. One issue you might run into though is the height of the tire. The outside top edge can rub the inside wheel well above where the lip is. You can push it out a little with a bottle jack or a BFH if needed.

There are a few early Valiant NHRA stockers running 255/60/15 drag radials with everything in the stock locations. Tight but it fits.