Could be wrong, but one of the reasons those tires work with 4 1/2 rims is they squeeze the sidewall in a bit. However, the tread width is about the same as the 215-75 15's I'm currently running on 15x6 rims and there's plenty of room for those.
Tirerack.com has a great site, pick out a set of tires and they list all the specs better than other sites...things like tread width, overall width, recommended rim widths, etc. Put all that together and you should have a pretty good idea of what you need.
One more thing, my 15x6 rims have zero offset, which means the mounting surface runs dead center to the rim width. Forget the meaning of "backspace" but if yours is 4 inches that could be the problem you run into.
Besto luck.
