1979 F350 Short Wheelbase with 9ft flatbed 10,000 lb GVW
351m original engine
C6 Transmission

In case it helps: VIN: F37HNFA0340

Are there any experienced ford people here who can verify whether it is possible, without semi-serious rebuilding like relocating motor mounts or maybe different bellhousing etc, to swap a 460 in where the original engine was the 351m?

And further, if I did such a swap and the 460 was in reasonably good shape would I see much of a difference on hills and such?

Currently with the timing in a known good state, it seems to do somewhat poorly on hills. I see smaller vehicles (and newer) with similar payloads blowing by me.

My engine is worn but serviceable. Last time I took a compression test I don't recall the numbers but only that it was pretty uniform... no more than 9 lbs difference all around.

I've experimented with retard and advance of spark by turning the distributor in very small increments while testing on hills, and think I have that set about as well as it will get.

 

I would suggest a search on "400 to 460 swap". There are alot of threads on the topic and it would save my lazy fingers some work. lol
Tranny bolts right up. L & L and Bronco graveyard have all the parts to swap it in (mounts, etc.)

If you are wanting to add power this is going to come down to rebuilding the 351m to a 400, or swapping in the 460. Lot's of threads on this as well.