You've got a pretty rare car!
The 544s were selling strong in 1960 and not many 122s were sold in the US until about 1963 when they came
out with the B18 engine, which was slightly more powerful and quite a bit more rugged.
I suspect that you will have a hard time finding an original owner's manual. They're hard enough to find for 1970s models.

Unless you are going for sustained high-speed operation like racing, you probably can get by fine
with regular unleaded gas. If your valve clearances start to disappear you'll know it is time to pull the head
and put hard valve seats in. Most automotive machine shops that can do a valve job can do this also.
--
George Downs, Bartlesville, Heart of the USA!