I just saw in my prior response I said 10/20 -- this should have been 10/40.
You don't have to buy special oils. Ordinary over the counter oils will do. I run Rotella T 15/40 in my 56, have made two trips from NJ to the west coast using this oil plus a lot of other trips to various CTCI conventions and locally. Absolutely no problems using this oil. I also use Rotella in my 312 powered 54 Ford (Newly rebuilt engine) and had no problems.
Same with my other cars with flat tappet cams. I use Castrol 20/50 in my 48 Ford (302 powered, non roller) and have made trips all over the east coast with no adverse effects.
You have to remember - the oils in the 50 and 60's had a lot less ZDDP than the oils we have today, even with reduced amounts, and there was no problems with camshafts back then.
Again, never use in a flat tappet engine those oils which say "For Gasoline Engines Only".
Midland Park, NJ
56 TBird, 54 Ford, 48 Ford, 64 Fairlane