Welcome
Welcome to the forums Dale,
I have put Corvette 8" rallys on a '61 (sorry can't remember the tire size). they rubbed in the front on hard cornering. Autocrossing. I put a wheel off of a '76 on my '59 in the rear with a stock 225/70 and it would touch with the slightest bounce. Back in the '60s we ran 15 by 6" Americans with 8.25/15 on the rear and 7.25 or 7.75 on the front with no problem.
I have seen '67 6" Rallys on the '58 to '60 with a stock looking radial tire, 195/70, 205/70 or 215/70, but there isn't a lot of room for anything too much bigger. I've been thinking about 15 by 6 American Torque Thrust on the front and 7s on the rear with a 205/70 on the frront and a 215/70 or 225/75 on the rear. I need to do some measuring. you might be able to order a custom offset and get the wheel centered in the wheel well for a slightly larger size and still keep the rubber under the plastic.
One of our supporting venders, SS Auto Sport, is a dealer for Wheel Vintique. I think they have a chart in their catalog and probably on line to show how to measure for correct backspacing.
I am very interested in what you come up with.
Send Steve at SS a message and see what he can come up with.
Tom