I don't see much problem with building a 450 Marlin on that short action.
I built two 458 Win mags on Savage long actions this year.
1st was a 20" stainless barrel on an older staggered feed action, originally a 7mm Mag. I didn't need to change bolt heads on this. I added a limbsaver, which was needed. I needed to bend the sheet metal mag box to feed better, but it only works perfectly with two in the mag, one in the chamber. If I cared enough, I could get a 458 mag box from midway. I had a 3x weaver, but changed it to a 2-7 Nikkon shotgun scope.

2nd 458 I built for my cousin. It is a new center feed action that was originally a 300 win mag. I kept the 300 barrel for a different project. The center feed action is much much much better! Feeds perfectly every belted mag I tried with it (7mm, 338, 458.) I acquired a new detachable magazine stock, with the new P.A.D. recoil pad. That new recoil pad is as good as the limbsaver. This rifle got a blued, 24" barrel. I put on a 2.5x weaver scope, which my cousin changed for a 3-9.
The 458 is a belted, long action round with very little body taper. The 450 Marlin is a belted, short action round with very little body taper. The 450 belt is slightly thicker, but I don't see that as a problem for feeding.
You will need a new bolt head, (buy a new extractor, ejector, and springs too.) The magazine box may need to be opened, use needle nose pliers. If you mess it up, Midway sells new magazine boxes. E.R. Shaw will make you a 450 Marlin barrel, you need the small shank Savage. You can buy headspace gages, or use new brass. Good luck!
As far as "brush busting," I read an article years ago that identified the 458 as the best, shot through branches into a target. I don't care, I wanted a 458, so thats what I built!