4th gem rear to 3rd gen car?
 

i have a 4th gen rear out of my 93 Z28 and i was wondering if it will bolt into my 91 Z28?or if i should just sell it???

You can use it but it will be wider than the third gen rear. That will create wheel clearance issues in some cases.

if you use a 4th gen wheels on rear, than it will work, but then you'll need the spacers for front to use the 4th gen wheels.