Lets see; the hydraulic lifter uses a pumpup port similar to the bleedoff part of the injection pump. Could just plumb a small reservoir of oil to the IP port, ?feed-return?, line. That would take care of the oil expansion problem. Adjust just like my old Chevy. Loosen up until valve starts clattering, then slowly tighten until noise stops, then tighten a specified amount more. Usually 1/4 to 3/4 of a turn. That puts the piston in the center of travel and gives room to both sides for expansion/contraction. Eliminates need for readjustment, eliminates a lot of valve noise, should eliminate a certain amount of wear, and takes care of the misalignment problem. Might use some type of bellows arangement at the valve itself. Would solve leakage problems at that end.
Andre, I think you've hit on a real good one.
AND eliminates need for another continuous flow oil pump.