does any one no the biggest wheel and tire that can fit a stock 77 280

Henry, do a search for wheel, tire, size. This has been covered many times here. Keep in mind that the factors that play into this are pretty much identical for the 240, 260 & 280Z from 70-78.

The most backspace you can get away with on a stock 280z is 4.5". As for front spacing without needing a flare, I couldn't say with any authority. I would guess that a wheel much bigger than 7-8" is going to want a flare to keep it from sticking out too much.