That's opposite what the tire will do in my opinion. larger base will extend the bead width but the cross section is fixed. Going to a more narrow rim may change that sidewall to a more narrow overall width (just because it has to reach back for the rim bead) but that is not recommended as the tire is designed for a specific size bead width. space your rim out 1/4 and roll that fenderlip with the lip roller that swings in an arc off the hub after carefully starting the trim flange to bend up. Looks like you have plenty more room if that lip is cleared, like most A-bodies.
