There are several things to unpack in your post, most or all of which have been covered by others, but sometimes it's helpful to look at exactly what you're asking for to get to the answer.
As it stands now, you're asking about changing everything in a big block of changes, which is kind of limiting. Why not take the issue step by step?
Wheel size. You have 15" wheels now. There are a greater number of modern tires available for 15" wheels. You might consider just getting new tires for those wheels. It costs you nothing and keeps most of your options open.
Tire size. As you mention, that is not the factory tire size, and except for Coker, the original tires aren't readily available. 235/75-15 is the size most of us run as being closest to original. You can still find them in the (reasonably correct) 1" stripe at a good price. If you go with Magnums and want blackwall or RWL, they are also available in this size.
Sidewall. 1" stripe is closer to correct for your car. Wide whites went out in the late 50s.
Hubcaps. If you just put new tires on your current rims, you can use your current hubcaps while you look for 15" 300 wheel covers. If you insist on "original" 14" wheel covers, you can modify your 15" wheels to accept the 14" wheel covers and still have access to the greater range of 15" tires.
Converting Your (Chrysler) Imperial's 15 inch Rims to 14 inch Wheel Rims. You can still buy Magnums later if you want, and will only be out a mount and balance charge.
Wheel Type. I like Magnum 500s, but I don't know how they'd look with white stripes, that's a question only you can answer. I don't know the cost of those or the cost of 15" 300 covers. But if you are set on them, getting tires for your current wheel setup means you're not pressured to buy the first set you see, and you can probably save a few bucks there.
So the only real recommendation I have for you is to go with some version of the 15" wheels. If it were my car, I'd probably keep the current wheel/cover package, get new 235/75-15 white stripe tires and start looking for a good set of 15" 300 covers.