I did finally get a chance to try to pull the pitman arm off, but no matter how I tried, it's not coming off while the steering box is in the truck.

I'm not taking the steering box out of the truck unless I'm replacing it, so...
Do I/ can I put in an HD steering box from a 3/4 or 1 ton truck, or am I stuck with the little one that's in there? The reason I ask is I'm going to eventually put a taller tire on there along with hydro assist, and since this box has a fair amount of play (270k miles plus rock crawling abuse) and is leaking, it's a candidate for a rebuild/replace. If I do hydro assist, will I even need the strength of the bigger box, if it'll even fit, because the hydro will take a lot of the stress off the box? Or will I need the bigger box to supply the valving needed for the ram?
It also needs power steering hoses.