Valiant & Dusters have the same wheel well size ??

I've never notice until I got my 68 Valiant that a Duster is just a fast back Valiant like they did with the 64 Cuda. I aways thought Duster was a new design.

Since the lower hind quarter is the same at least it looks it to me. Then it would have the same rear tire size capability ?
And what would that be stock ?
I think I've heard 275 is the biggest.

I've always heard that duster has more room than dart.