but are dana 60's (rear ones anyways) really that much of an upgrade from stock? Perhaps some rockwells/eatons or 70's?
Or if you really want to do it right, mog axles. But I have no idea what kind of power a mog axle can take.
Well, yeah! The stock engines put-out a max 155 HP on a good day!
That said, the stock, 30-spline TLC axles and diffs are plenty strong, though 450 HP is way outside their design criteria!
What transmission will you be using in the rig? An automatic offers some "buffering" of the shock load in the drivetrain from excessive use of the "skinney pedal."
Still, with 38.5 inch Boggers and 450 HP I'd suggest finding a 1970s/80s one-ton GM/Chevy 4wd pick-up to steal axles from; that would net you a Dana 60 in the front and a GM 14 bolt in the rear - both plenty strong for your use.
If you want to be different, and practice the art of over-kill, a pair of Rockwell axles from a 2.5 ton army truck would be cool!