I have a motor that seems to be a '69 Z28 302 top end- rebuilt on a 283 block bored to 301.  Manifold, heads, carb, cam all seem to match the 302.  The problem is this motor needs a lot of rpm and has too much compression for the street/rod use I am planning.  Question: are these heads worth reusing with a 350 block w/flat top pistons [est. 9.5 to 1 compression] and will it give me good torque and 300+ hp?  would I be better of just gong for a 350 crate motor with modern heads?  

alot of things have happened in head designs in the last 39 years... if money permits go with modern parts...

a mild cam, a good set of modern heads with alumnium intake, and a set of pistons that will bring the compression to 9.5 to one (search for online for a compression ratio calculator and play with the numbers to get familiar with how they interrelate)and you will meet your goals

as for the crate motor you will spend more money and will make a compromise of what you really want when compared to what you could build... but only build if you are experienced or know somebody who is that will help you throughout the build