I've noticed that few Americans like set triggers. Maybe it's because we don't have any familiarity with them.
I started using set triggers at age 14 (Now nearly 70), and I shoot much better with the sets. It was one of the things I liked regarding the CZ 550s I had, 416 and 375.
Regarding souping up the Rigby, I was under the impression that Rigby brass was far thinner and it wasn't a great idea, accordingly.
I had a lot of experience with the Rigby years back and shot coyotes here on my small farm with both CZs and a Ruger RSM with my reloads and 350gr Speers at 2,575 FPS. I had a CZ hogback model and an American. I actually liked the hogback better for me; it just fit me better. I didn't like the Ruger stock much, but I loved the rifle otherwise. The buffalo in my avatar was taken with a CZ550 Rigby hogback.
After shooting considerable 416 Rigby ammo, factory and reloads, I am a bit curious why anyone would want to make it hammer their shoulder and brains any more than with traditional loads?
You must be young and tough.
Have fun with a great rifle in a Classic round.