I've had issues with both GN1 and TA aluminum heads with oil drain back. On my next rebuild on a StageII with TA heads, I will drill through the lower aft corner of each head and run a -10 AN hose down to the pan. Can do the same with Champion heads I think.
I usually drill the rivets and spray copper coat on all layers of Cosmetics. At a minimum I smear sealant around the end layers and around water ports.. Never install completely dry as they suggest.
Eactly what I would recommend. I also reduced the hole in my push rods when I ordered them. When I did the mockup on my TA heads and TA block I did a fair amount of grinding on the gasket (not Cometics) , block and heads to make that drianback hole larger.
I just finished cometics on my TA heads the way Turbofabricator has explained. I'll see if it leaks and report back. The last cometics wept water, so I had to run tabs (that helped a lot). They also leaked oil on both sides.