will a 69 f85 rear clear glass fit a 70 olds cutlass post coupe rear

 

As long as they are both 2dr cars.

 

rear rear glass I believe so

rear side glass only if both are post cars.

Do you have a PN manual? Wildaboutcars.com probably does.

Gr. 11.204, Glass, back window
find your model, then see what other models used the same PN...

 

The rear window glass and stainless trim is the same on all 1968-72 3XX77 and 3XX87 bodies (that's all Sport Coupes and Holiday Coupes except the 70-72 Supreme). Note that the rear glass is NOT common across other GM A-bodies, however.