You have mentioned rocker arm assembly oil flow but did you see if all valves are moving properly. I apparently didn't snug the rocker assembly bolts after replacing bent pushrod from stuck valve. Engine ran fine at first then started popping back thru carb. After trying several of the steps you refer to I pulled the cover and found some valves weren't moving. Tightened the nuts and problem was solved. A very slightly bent push rod may not fully open valve but still stay seated in rocker assembly.
