Well people kill bears with .22s but I won't plan on it. I want something larger more powerful.
All kinds of ways to increase towing and stopping power.
If your axle is heavy enough, and I don't know if the axle with the 351 is the same a diesel or not . If you can find a used diesel differential axle brake, for a wrecked or scrapped vehicle would be good. The gear ratio might need changing in the speedmeter. Same with the trans. If you want to stick with gas Ford has crate engines up to 570 inches I was told, but certainly some over five hundred inches. And a heavy duty tans, radiator and oil and trans coolers. and changin brackets etc for air and brake booster. Probably 20,000.00 or so.
There are or were companies that specialized in installing diesel engines and drivetrains in gas pickups. I looked a t a couple of laces when I had an85 Dodge 4x4 but never did any changing.
You can haul it with the 351 but it will be strain and over rate for your truck and in some places perhaps a ticket.
Perhaps you can find a decent07 or earlier Dodge Dualie Diesel with no cats nor no pig pea tank. Almost bought one two years ago with 7,000 miles on it with fifth wheel hitch and everything for 27,000.00 or half a new one.