About the compression loss: The only way I can imagine a head gasket causing this would be if the head gasket is thicker than the old one. Then the total volume in the combustion chamber would go up, so the compression would go down.

Or, did you clean the pistons off when you removed the head? If so, all that carbon buildup on the pistons will raise compression some; scrape it off and compression goes down.

Lastly, if you set the valves without enough gap, the valves will never close fully, and the engine can't develop compression. You will also burn the valves.

Is power down? Did you rebuild the head when it was off? A leaking valve stem seal could be the reason for oil loss. Look for a puff of blue smoke when you start it, or if you let it idle for a long time and then rev it up. These are indicators of a valve stem seal.

Good Luck, I hope this will help a little.