Head lap

No not head in lap, but head lapping... So I searched and cant find any posts that tell the details of this process. Ive lapped valves and flywheels in the past.

I'm assuming I put a tiny amount of lapping compound on the horizontal mating surface of the cylinder, put the head on and then rotate it back and forth a bit with a little pressure?

Yup put some lapping compound on the surface of the seal and turn the head right and left, lift the head up draws the lapping compound back to the seal area and repeat. With a little pressure. Once the seal surface is completely a light gray it's done. Now there is a course and fine lapping compound use the fine lapping compound. I do this on every engine I pull the cylinder on.

At the same time while it's apart take a straight edge and check the bottom of the cylinder and the case base gasket area for flatness. Make sure there are no burrs. I seen where the PO have used screwdrivers to pop up the cylinder leaving a burr on the edge of the base gasket area. The leak down test will make it show up but it's better to look for it while it's apart. Check and double check.