The better test for checking the oil flow is to turn the motor over very slowly while running the priming tool until the holes in the cam line up with the holes in the cam bearing. At that point oil should come gushing out between all the rockers.
If it doesn’t, Ive seen some builds where a couple of flats were ground into the area of the hold down stud adjacent to where is passes through the lower portion of the shaft.
You could also ream the lower hole on the shaft at the #4 stand about .030 or do to make a larger path for the oil to enter the shaft.

I can’t see it being the size of the oil passage in the heads....... EZ heads also have rather small passages....... no oiling issues with them.

One of the best tests (imo)to check oil flow up top is the old steel valve cover that’s got the top cut off, so you can see how the oil is flowing with the motor running.

All that said....... if your only symptom of a problem is smoke coming out of the valve cover breather, and everything inside looks good....... maybe there is no “problem”.