The Diablo is garbage.
Completely forget about it.

The 20/20 pedersoli Howdah is fun, mine is barrel-spacing accurate with 70 grains FFG and tightly patched hard roundball.

That pedersoli Alaska Howdah looks interesting.
I have a contender barrel here in 410/45 that I have loaded straightened 9.3x74r brass and well over 60 grains rifle powder and .452 bullets. Ridiculous power. Ridiculous recoil. Far more energy than you can get from the 20bore caplock.

Then there's the big bore revolvers.
A 5-shot 500JRH is far more handy than the X-Frame S&W
I'm building one on a Redhawk, and I've built one on a Ruger Alaskan, I've built many on Blackhawks. With top loads there's no bovine that can stand the cartridge.

Just some thoughts.