I've got three converted to 45/70. A better one than that would be 450 Marlin. Reason is when you load a rimmed cartridge down into the magazine, you have to make sure the rim of the next round MUST be positioned ahead of the rim of the round underneath. If not, will. be a certain jam.
I've got a Ruger 77 (tang safety) and a pre 64 Win 70 both in 450 Marlin and don't have the rim overlap jam worry. I really believe if the 450 Marin had been on the market when all those Siamese Mausers where coming in, the 450 Marlin would have a much greater following.
You may well be right for the Siamese. They did work when loaded from a stripper clip. So; I dont know. I believe the effort to one up the 45/70 failed to appreciate what a fine round this was and continues today. it has always been better to load your own than pay the big bucks for limited factory offerings. The reloader has no need for 450 Marlin in a Marlin lever. Or buy hot loaded 45/70, it is available.
The final straw was the idiot proof unique fat belt on the Marlin. How sweet if common belted ammo could be cut down to make Marlin cases. And even fire marlin ammo in a 458 Win. That belt was pretty much a deal breaker right there. Might as well build a light weight 458 Win and load to Marlin levels. I though the industry missed a bet, in not loading a reduced 458 win for NA big game. You would have seen a lot less 458 WM on the used gun rack.