Re: 455 + box blade/scraper -- dealer says don't do it?
Not sure what kind of tree that is, but if the roots are near the surface, they'll stop you dead in your tracks. If you hit one, you could try and cut it with an axe, wrap a chain around it, and pull it out of the ground. I think other than that, you should be able to get it done no problem. I can drag my heavy hitch ripper up to the hilt through my rocky clay hardpan without too much issue. It'll pull up some pretty big rocks, but I have all kinds of ballast. The front blade for a 445 is 54 inches, and can be locked out for dirt work, and I've used mine to good effect, so I don't see why a 4' box would be so bad. The loader bucket is also 4' and designed for dirt work, so I think you're safe.
Herd of Deeres:
445 with 54" & 60" decks, 54 Power Flow, 47 snow blower, 54 blade, Curtis hard cab, weights, chains, loaded turfs, v61 fronts.
445 with 40 FEL, cat. 0 3pt, rear pto, 4ft bush hog, heavy hitch, loaded Tru Powers, v61 fronts.
140 H3 with 48 deck, 54 front blade, 54C grader blade, loaded Firestone 23 deg. rear ags, loaded tri-rib fronts
140 H3 Spruce Blue Custom Color with Haban Sickle-Mow. Restorations in progress.
265 with 48" deck, Power Flow with JRCO cart, 30 mech tiller.