Had heads reworked and milled. Put back on the car with all the right specs. Started car and within 5 minutes was blowing white smoke. Dont get it. New head gaskets, reworked heads... It runs smooth, just smoking.
Any ideas?

Sorry this doesn't answer your question but make sure you get your coolant flushed out and replaced (Dex-cool). You might get some oil in your coolant after any headwork so pull out your coolant dipstick and check it out.

try running some seafoam through it if that don't work check your piston rings...

Depending on how bad the original condition was, there may be some coolant still in the exhaust system that needs to be burned out.

Have you done a compression and leakdown test on the engine(pointing to the rings like the gentleman above)? How long did you run the engine after the smoke started?

How many miles on the bottom end and has it had a rebuild?

This would be my initial thought as well.