Yeah... it's kinda hard to say what would happen without actually trying it out. Bruce of BCM told me the new style is more cooling effecient for the entire cylinder, as the area the oil occupies would allow trapped air.

I lean to think that there wouldn't be much difference to have the oil drain or to simply plug it off so long as the oil return on the bottom of the cylidners are identical.

Also, I suspect that the drain lines are on the return side, not on the pressure side, so they have nothing to do with the pressure in the heads...

chris