Good rule of thumb is to match the tread width of the tire to the width of the rim. So a 275 would fit best on an 8". 295 would fit best on a 10" Of course since there are a number of 9.5" rims out there, you can blurr the line a bit. The car in my avatar has 295s on an 8" rim, but to get a full contact patch they have to be run at 20 psi, which is a bit low for optimal performance.
Others have done 10" wheels with minimal mods, but tire width choice, as well as wheel backspace, may also make a difference in that scenario. The most popular seems to be the 1" relocation kit with a 66-67 B body rear and a 13" section width tire. I suspect a 15x10 with 5" back space and a 295 tire can fit with no mods, but it will be a VERY close fit, and I have not physically done it to verify, although I've got the wheels sitting in the garage to try.
