Interesting, I was just looking at a copy of COW and the 458-2" wildcat caught my eye. A friend had built one in the mid 70's and it was one of his favorite deer rifle, tracking/stalking. You should have no problems with your build as the 450 Marlin and the 458-2" differ very little (Marlins odd belt). Personally if your a reloader I'd build the 458-2" as you can cut down any of the standard mags for brass.