Great info here.

Anyone know what happens if you go the other way around and put a protruding head on a recessed valve block? I ask because I just assembled a motor with a short block and head from china. The head is protruding. The block, to be honest, I'm not sure. I asked the seller to sell me a block that went with the head I ordered(I did this all on aliex) and now, when my motor is up to operating temp there is a horrible tapping, like a collapsed lifter in a hydraulic lifter setup. I've adjusted valves and timing so many times it's ridiculous.

Anyone have any pics of what a protruding valve piston top looks like?