Didn’t read the entire thread, but I own a similar 1999 F450. Mine has a Boss straight blade plow, v10, and automatic, with about 73000 miles. I bought it at a municipal auction in 2007 for $4500. It was a former Park District truck, and cheaper than F250 pickups in equal condition. The suburb I lived in outs Chicago had an excellent maintenance program.
I listed it on Craigslist about a year and a half ago for $6500. Had second thoughts and withdrew the listing, but my email lit up with interest. One guy drove 350 miles one way to look at it. He tracked me down even though I didn’t give an address. He had a pocket full of cash and was pretty disappointed, to say the least when I wouldn’t sell.
Cab corners, inner and outer rockers are simple to replace. The corners can be replaced using structural adhesive, rockers are simple to mig weld in. Door bottoms are available, but southern doors are available from entrepreneurs in most little towns.
Downsides are the gvwr of mine is 14500, so legally I need a CDL to tow my 14000;lb trailer, and Michigan license and insurance is expensive, since the gvw of an F450 pushes it into commercial territory. Good news is that plates are available in quarterly increments.
I put brakes on it, repaired broken exhaust manifold studs, replaced one battery, a starter, and one tire over the 16 years I have owned it, as well as oil and grease on a sporadic basis.