I would use a higher zddp oil.
More info is needed... what cam/lifters kit, what valve springs? what oil pump? oil sump size and/or cooler?
what oil filter? typical oil PSI and temps, especially when being worked? what engine builder and specs?
Ford has a good list:
www.fcsdchemicalsandlubricants.com
Not all euro oils are higher in z/p levels or hths so be selective with the spec.
Castrol A3/B4 oils are sometimes available at some walmarts and are a great choice. Mobil1 0w40 is another.
I could care less what engine builders recommend since most are clueless concerning oil, like most mechanics too.
Since you're using RP, why not just use their:
https://www.royalpurple.com/product/hps-high-performance-street-motor-oil/ unless the interval chosen and/or availability drives costs up too much
The Rotella 0w40, 5w40, and 15w40 in conventional/blend/synthetic are excellent choices and probably one of the easier to find oils. The T4, T5, and T6 are really good, for your cars, generator, mower, tractor.... and won't break the bank. Rotella T6 5w40 is an easy to find choice.
The mobil link below is their downloaded pdf z/p content for some of their oils. A single quart of 20w50 V-twin or their racing oil can spike a sump of greenie API oil more than enough. The 5w50 and 15w50 are pretty stout and the turbodieseltruck 5w40, if available locally, is a great choice.
For example, my last oil change in my VW was 1 quart of Amsoil Dominator 15w50 and 4 quarts of VW 508 0w20 oil. The little z/p spike and visc are what I wanted.