I didn't read all of the responses, so forgive me for repeating what may have been said.
I've been using Brad Penn in place of Joe Gibbs
oil for a couple of years from breaking in engines on the dyno and using it on the street and track in my three flat-tappet cam engines, a stroked 302, built HP289 and a 427 side oiler. For a backup, I've ZDDP additive from ZDDP Plus Central in other premium oils. Here's their web site:
http://zddppluscentral.com/home.
It's improtant to note that the most critical time with a flat-tappet engine is during break-in. I know of many engines that have wiped out their cams during this intial running period, or break-in and the first 500 miles. I've heard it said that you can "get by" without the correct amount of ZDDP in the engine
oil once fully broken in, but I don't put this off to chance considering the consequences.