Homer - I have an article on the .416/.350 Rem mag. or .400 2"-somewhere - maybe that's what it was called. The 2.1" case of the Marlin would be fine as well, but restrict you to that brass.

Interesting round.

Here it is, by A.O. Winters - the 10.6x51 or.40x2". It seems to be a .416" bullet as he also calls it the .416x2" was designed by necking down .458x2" brass. As I found necking up .350 RemMag. brass for my .458 2" was much better, that is what I'd do.

So - this .416 - he kept the pressures moderate - according to his Powley Comp., under 53,000CUP, which in this case, being so similar to the .45/70, we know that number will be virtually identical to PSI. Actual loading is the only way of determining safe loading practises - of course, as always, start low and work as pressures indicate.
270gr. custom - 2,449fps
300gr. custom - 2,332fps
330gr. custom - 2,211fps
400gr. custom - 1,896fps
At these levels, it would be an easy shooting round.
Due to the chamber shape, 400gr. were deemed to be too long and appeared to use up too of the available much powder space, much like using 500gr. in the .458 2". Much depends on the throat and leade.

A good and fun pig ctg.