I had a '69 K5 before my XJ that I swapped a '95 Police Edition 350 in there.
...much easier as the stock engine was a 350...

But still a PITA (at my skill level) to get the fuel lines and pump... and computer work... and wiring...
Minor cutting and welding for tranny/transfer case mods...

But it ran like a MoFo!

Weight to gain ratio in an XJ!
That'd be reDonkUlus