Cheaper than dirt 318 build

Mid 1990's to early 2000's running trucks and Durangos with a 5.2 or 5.9 are usually plentiful and relatively cheap.
Part of the reason is that during the era they were made no one, repeat NO ONE could make an automatic transmission that was any good.
You will likely find these trucks that run but do not drive or drive poorly because the transmission is in need of being rebuilt, possibly for the second or third time.

The "Magnum" engine has moly rings and coated piston skirts. Both are a plus for longevity.
The Magnum head is far superior to an unworked LA head, and we all know a LOT of the power an engine makes is because of the head design.
They are designed to run on "pump gas". Even 87 octane.
The hardest thing about swapping a Magnum is finding the ancillary items detailed at the magnumswaps.com site-
Oil pan, timing cover (if converting to LA style), fuel pump eccentric, balancer if required, bell housing, etc.
Magnim engines are usually still running fine well past 100,000 miles.
My 2000 5.9 runs like the day I bought it and has over 177,000 miles.

It's a fairly "easy" 100 HP gain for less than the cost of trying to get a 100 HP boost on an LA build/re-build.