I recently acquired a 1977 280Z that is 100% stock. I want to make a few upgrades to help with performance and appearance. It is due for tires and I would like to purchase a set of the Rota RB's wheels as well. I want to purchase as large a rim tire combo as I can without any modification to the car. I also would like to get rim size that gives me the largest selection of tires. Ideally I would like to purchase the tires and wheels from one vendor so they are complete when I get them. I appreciate any input.

That's a complicated question, 15x7 zero offset wheel with a 225 50 15 tire clears. 16x8 wheel zero offset fits but I think you are limited to a 215 width tire, there are people running 17'x7 wheels with a 205 width tire obviously a lower profile. 15's and 17's offer more tires than the 16's these days, Might want to give MSA a call they sell wheels and know Z's better than anyone. zcarparts.com

A buddy of mine has 16 x 8 with 205's on it and it fits great... not 100% on the offset off the top of my head

Thanks for the feedback, I ending up going with the 15x7 with 225-50-15, this is what MSA suggested.