The part that I find puzzling and also the part that indicates you should look elsewhere is the fact you assembled the top end after the porting the same way you did prior to the porting when it ran without significant issues.
The oil behind the intake valve is indicative of a loose guide in combination with a failed valve stem seal. You will get smoke on startup from the accumulated oil which typically goes away right after startup and doesn't smoke on acceleration. On deceleration, when you will get a puff of smoke that disappears as soon as you're on the gas again.
Honestly, the whole thing is puzzling. It almost acts like an overfilled (oil) sump.
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Triple Black 1971 GTO
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