Not exactly what you're asking, but I have a custom Ruger No.1 running smokeless jacketed 45-120. I have run cast and black powder for fun, but this thing gets up and boogies running smokeless.
My steel targets, not AR 500, get hammered by this thing at 200 metres. Far outweighs 45-70 rounds…
The 450 Marlin is probably the longest cartridge you can house in a regular lever action.
The Ruger No.1 or falling block made by the old Remington bought company which I forget their name, owned originally by Art Alpin do a nice falling block, Ron Spomer has one in 7x57.
Cheers.