If you have stock wheels, Don is on the money with the 215/70/15
Depending on the trim package or what car it is from that era, it may have had 205's on 15x6.
If you are getting different wheels, you have some options. 5x4-1/2 bolt pattern.
I went with 15x7 in front, and 15x8 in back, Crager D-window wheels in black. Like this:
Free Shipping - Cragar Black D Window Wheels with qualifying orders of $109. Shop Wheels at Summit Racing.
www.summitracing.com
Chrome lugs, I bought centers but don;t really like them, going to either just paint the hubs black or maybe find some chrome "spiders" that go on the lugs.
I chose a 4" offset up front, but I went with the 4.25" offset in back for a little more fender/lip room. I put 275/60/15 in back. Plenty of room. Up front I went with 235/70/15. narrower, but this kept the same wheel height which was important for me as mine went on an old police sedan. Didn't want to rake my 4 door lol.
This was a 78 Monaco sedan, YMMV with a 77 2 door charger. I suspect with proper rims the 275/60/15 would be an easy fit, but with stockers or the wrong offset they may not. I don;t have first hand on the 2 door cars.
The Cragers have gone up in price(what hasn't) since I got them a few years ago. I paid around $550 for the wheels and tires before everything went nuts. Probably more like $800 to do it now.