I think the backspace on a 10" wide rim needs to be 5.5", according to guys here who've done that.
Belvedere body has less room than the Coronet & Charger because of the outer wheelhouse.
I've run a 295/50 R 15 on a '68 RR, on a 15x8 4.5" BS, plenty of room all around; I think the bulge was about 11.25".
Classic interference point on Mopar wheel openings - rear & front - is at the front bottom.
Also check the contours of the inner.
A straightedge, tape measure, and a spare wheel are handy for measuring, as side/side may differ.
A bit too much BS is easier to remedy with a spacer than if BS is not enough.
All the above is stock locations, openings & wheelhousings.