I was thinking some more on this. Do you have restrictors in the head
oil passages? As above:
"
Oil flooding. I always had restrictors to the heads. If you don't, keep in mind the engine sits at a slightly raked back angle and the rear valve guides could be swamped with
oil."
It's the easiest change to make at this point. First time I did it, I machined aluminum rod and drilled a hole through the center. Last time I used allen plugs with a center hole, but you don't want to do this with the engine installed as metal chips will get into the oil passage. All you really have to do is cut 1" sections of rod the fit easily doewn the oil passages. Enough oil will come up around the rods.
It only involces removing the valve covers and rocker assemblies. For testing, you can probably re-use the valve cover gaskets. If you still have problems, then it may be the manifold gaskets/manifold maching as a next step.