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You're planning to swap the heads to what? Does it have the original 920 castings? If they're not cracked, they're not a bad head if you can run high enough octane gas for them. The later open chamber 675's seem to be less trouble prone, but, they'll lower your compression ratio a bit. If you're putting in new pistons, that can be overcome. The late model 302 casting are also a good head for performance and mileage, but, you have to plug the smog holes and do a bit of grinding on the driver's side to get a stock exhaust manifold to fit properly. If you're keeping the stock 2bbl pistons, don't over cam the motor. The stock 4bbl cam or slightly less will work fine. I have a .435/.435 Isky solid cam on a '68 2bbl engine with the stock '66 4bbl intake and exhaust manifolds, and it works fine. No need for headers with that setup.