[James]

I would pull off the rocker arm shafts. They could be full of sludge, which will starve your valve train of oil. You may want to look at the hole that supply the rocker arm pedestals (the end pedestals for cylinder 1 and 6) to see if it is plug too.

The oil supply come up from the cam bearings through the heads above cylinder 1 and 6 (In fact it is the hollow head dowel pin that feed the oil to the heads).

Assemble the well oiled rocker arm shafts back onto the heads, check/set the valve clearance. After you do that, continue rotating the engine and take note on how far the valves are opening. They should be opening about the same amount.