I own a bmw z3 1.9 1997 and just aquired some wheels from the z3 2.8
but i notice the rear wheels are 17" 8.5J
will the rears fit ok?

all bmw wheels fit all bmw cars

As stated all z3 wheels will fit an year of z3.

Try using http://www.tirerack.com and match up the numbers or you could call a BMW dealer too.

Good luck.