I'm having a similar problem with my 426 W. DLI crate motor from 2006. Like you, NO smoke on start up. Compression test all cylinders range 185-200. Spark plugs showing oil on left bank only. Right bank even tan/brown appearance. Smokes only after stabbing throttle hard, never at idle, start up, or cruising. New valve seals 2 years ago (because I could). Baffles are present in valve covers. Bore scope shows some carbon on piston tops. Oil in intake manifold mostly on left side, and in intake runners on left side. Malfunctioning PCV system will cause buildup of crankcase pressure under acceleration, and oil may blow past a seal or gasket. The intake gasket is in place, and I must say the port matching job done at DLI is perfect, and the steel intake manifold to valley gasket is visible. The oil residue is heavier downstream from the gasket on the floor of the intake runners in the head on the left side and on top of the one closed valve I could see well.
It seems obvious to me the oil is blowing past the valley gasket on the left side. Turns out the intake manifold fasteners were at 35 lb/ft when I checked, so I retorqued them to 50 as specified in the torque specs. I have no confidence this will reseal the gasket, but I have had local opinions supporting the idea so am trying.
The larger issue to me is WHY am I running a teenie tiny PCV valve and hose rather than racing type open breathers with filter/screen. My deal is certainly not stock, as evidenced by the high compression. I will not be replacing my PCV system. It is an early emissions deal from the sixties which has no place on a high compression performance driven engine, and maybe has resulted in a problem due to oil blow by due to a loose intake manifold.
Carbs are easy to remove, Plugs a little fiddly on a big block B body, but doable. A bore scope can be borrowed or rented.
I am not yet back together. Waiting on NGK V power 6 plugs, which don't seem to be in the system any more, but my NAPA guy seems to think he found them and are back ordered. So the results of my detective work and crude mechanical abilities is yet unknown.
Good luck with your deal. I hope you find the culprit.