I have run them as lean as 20:1, but they like the rich mix just fine. Is your engine an A400? If so, it has no ball or roller bearings in it.
Stick with 30 wt NONdetergent oil, and I suggest you stick with 16:1 mix. They are not making parts anymore, so keep them lubed.
I have a NEW custom aluminum mount for that, and Timothy Taft on Facebook makes custom headers, very nice and very reasonably priced.