Just my not very humble opinion. Get the .450 Marlin as a collector's piece and buy a 45-70 #1 as a shooter. You can hand load the #1 45-70 to be just as hot as the .450 Marlin which, again in my opinion is nothing more than the old .458 Win. 2" wildcat. All marlin did was put a fatter belt on the case so reloaders could not use .458 Win. Mag. brass trimmed back to 2 inches.
My Ruger #1 is in 45-70.
Paul B.