A 295 width should have a 9"-10" rim width, ideally.
I ran 295/50s on 15x8 Ramcharger wheels on a '68 RR (Hemi/4speed/Dana) and had plenty of clearance all around.
Those wheels were 4.5" BS, stock wheelhouses & springs.
Spring location is the same width - whether Belvedere/Coronet/Charger - and I'd bet the inner wheelhouse dimensions are too.
I'd mount some bare wheels & break out the tape measure and a length of straightedge, maybe a plumb bob, and verify what BS is needed.
There's been at least one member here with a '69 GTX who ran 295/65s on 15x10s with 5.5 BS without problems.
Coronets have more room at the wheel opening, of course, so 5.0 or 4.5 might center better, but a wheel opening flange is quite effective at scoring sidewalls...