Slot Mag Question

You never said what look you want. With that wide of a wheel, it will generally be a reverse or very negative offset.
This will not clear a stock with rear axle at factory height without rubbing.
So either you will need a higher arch rear spring setup and longer shocks or a narrower axle to keep them in the fenderwell and the rear end down.
If you insist on this setup there should be local custom wheel sellers and wheel repair shops in your area that do wheel polishing.
I sold E-T Mags in the mid seventies. They were a good, high quality wheel.
So I’m going for the mid-70s look, 295 size tires in the back, sticking slightly outside of the fender well. The previous owner put in leaf springs that have five separate leafs in them. I’m also installing polyurethane bushings into the leaf springs. Suspension will be stout enough that the car shouldn’t have too much body roll. The car sits high enough now that a 27 or 28 inch tall tire should fit without hitting the fender lip. Not everyone’s look, for sure, but I wanted to build a 70s type street freak. I have a nicely built 383 that will be going in hopefully in the next few months.