Just a couple of random thoughts on recent posts.
Now I may not be exactly correct here, so allow me a bit of latitude:
While a cartridge .500 or .577 bore modern Howdah would be more “period correct” and (to a certain segment of shooters) desirable, this would run afoul of US Federal Law.
Anything over a strict .500” groove is (with “sporting” rifle & gun exceptions) considered a “destructive device” and subject to those rules, regs, and arbitrary Fed interpretations.

As to .45-70 -vs- .45 Colt:
People will buy what they know, and a .45-70 handgun is often viewed by “Joe average” as being completely silly & totally unshootable. Yes, there are a few .45-70 revolvers being made, but certainly not the norm.

Remember, this “thing” has to appeal to enough of a mass market that it will sell, and I’d be willing to bet that .45 Colt would be a better seller to people that would not know a Howdah from a pipe wrench (spanner).

Would I want one of these as presented? …..No.

Just my 2¢
- Mike