When the 450 Marlin was first released I was very excited. Not because of its potential as a levergun cartridge, but its potential in a short action bolt gun. I shot a lightweight custom 458 American once and loved it. Alas, the 450 bolt guns that were produced were few and far between. To me it would have been the best use of the cartridge. In levers and single shots the 45-70 is just the better choice.
In the end I did not want a bolt 450 Marlin enough to convert a 350 Remington Model 7, or to buy one of the few bolts that did come to market. I think Browning made one briefly in their custom shop as did Sako, both pricey. Im not 100% sure though.
I still love the idea of a short action Savage, stainless, with a high quality composite stock and an 18 inch barrel, in 450 Marlin. Would have been easy for Savage to make, and would have sold decently I believe.