I have just got some advice from my Gunsmith and he says the Pedersoli or Merkel conversion can be done but with recoil of .45/70 the web of my hand may get cut by top opening lever this may or may not be a problem . I would go for a under lever opening lever but I know of no modern firearms made like this . I am looking at the moment to the following

Pedersoli/ .577 Snider
Merkel/ .500S&W or .577 Snider

I have a Smith & Wesson .500S&W Magnum revolver on order and when I get it I will see how this round is in the recoil department (I think it should crumple a tiger trying to get in a Howdah). I will most likely go with the Merkel /.500S&W combination (it is not British but it is available) as I see this as a modern version of the Howdah. I am not sure of Barrel length 10" or 12" maybe, sights would be express style , any one who has any ideas on barrel length,sights,stock,calibre choice please forward your suggestions. Thanks
RLI