Ford Super Duty (1999-2016) :: Engine Swap 2006 F250 5.4 To 1000 7.3 Trans?

My dad has a 2006 F-250 5.4 3v that spun a rod bearing at 107,383 miles. He's never been thrilled with the performance of it (told him he should have gotten the 6.0 when he bought the truck new, but why listen to a 15 yr old ). We've been throwing around a couple different ideas for engine swaps since the 5.4 is dead. We scored a 5.4 2V Lightning engine, but after trying to figure out transmission controllers or if we'd be able to tune the stock PCM for the 2v, we've put the project on hold.

Recently, I've been trying to convince him to do a diesel swap over the L-motor. I have a friend selling a cheap 99 7.3 with trans, PCM, harness, intercooler, piping and other misc stuff. Would that harness generally be plug and play with the body of the 06? Would it be more worthwhile to try to find a 6.0 from 05-07 and swap everything over?

I've also been considering a Cummins swap, although I haven't gone much past looking at complete engines on eBay and Craigslist. Would this be the better route, and just get a standalone controller for the 5R110?

So I'm looking for other's opinions. Should we go 7.3, 6.0 or Cummins? Should we stick with gas over diesel? Try to make the Lightning motor work? Or just go back with a stock 5.4 3V? I should say, he won't sell the truck for whatever reason, so he's not worried about resale or anything. We're in Michigan, so we don't have to worry about emissions. And we're fairly mechanically inclined, so I'm not too worried about doing the swaps, however my knowledge on diesels is limited.