I've seen 1st-hand separate issues that all created a smoking issue in 426 Hemis:
1. Guide seals: remedied by switching to hi-temp silicone umbrella seals, which were blue in color.
2. Big cam/low vacuum upsetting the carb enrichment rods to the point gas would wash the walls.
3. The spark plug tubes letting oil into the chambers as already mentioned; had to lose the sealing rings & replace the gouged tubes.
Sounds like a lot of leakage past the rings on the OP's motor.