Oil choice for 1962 Lancer? What do you use in your Slant Six?

Read this and this. It will also be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads.

Oil (and filter, and spark plug) selection are topics that start bloody religious wars. Opinions vastly outnumber facts. Have a thick skin and take all advice with a Super Big Gulp of common sense.