I shot one of the Marlin carbine 18 1/2" 45/70's that looked kinda like that one, but think it had a regular lever.
The load was 49gr. RE#7, seems to me, with a 400gr. Barnes FN.
That load was listed in Speer's book with a 400gr. Speer FN, at 1,830fps or so from a 22" bl.

From Gord's short "Guide Gun" Marlin, it ran 2,004fps. Gord had told me earlier that it was 2,007fps with the book load and I said "bullshit". So, we repaired to the range and that's what I got on my Pact Timer, 2,004 fps.

I very much prefer my Model 86/71. My stock has much nicer wood than this one.

https://marstar.ca/wp-content/uploads/2019/04/PD-S.740-457.webp