The 68 144 should have a B18B with 10.5:1 compression and SU HS6s on the ugly one piece cast iron manifold. It was rated at 115 HP, by the standards of the time (SAE Gross, which runs about 10% more horses than a modern rating) Yes, 92 or 93 octane is recommended---the owners manual calls for 100 octane, but that was measured differently then too. A lead additive will put off for a while the need to have hardened seats installed. I think the B20B was rated at 125 HP, with a comparable increase in torque.

There should be a thick cork gasket between the valve cover and the head. It will seal pretty well if the cover isn't bent and the gasket is fresh. Sealant only makes for a lot more work the next time you need to replace the gasket.