I am never going to find the 151. It's just not going to happen. Though the 121 may be a direct swap from the sound of everything. I live in a weird area where all the common stuff to you guys is something I want but it never shows up here. Instead, all the super weird rare junk grabs my attention first and it's kind of what was mentioned:
Buy junk Wrangler
Pull 4cyl
Put in 8cyl
Profit
That's the common idea, right? It's NOT happening to the old Wranglers like I expect. It's happening to these old DJ-5s that probably have over 2 million miles on them or so. Some oddball gets ahold of a sweet decomissioned delivery truck, strips whatever paint is left, pulls the engine(and MAYBE the transmission), puts in a big I6 or V8 block and it becomes a high speed ratrod. After a few months the transmission or starter clunks out. They can't figure out why this happened and they give up looking for parts. The drivetrain gets sold for cheap scrap. This is an incredibly easy fix. I can do it to the late Gremlins, I can do the same to a Hornet or Eagle.
I checked out some old VW vehicles at an auction yesterday and was disgusted by how much is wrong with them. Busted hood latch, busted inner door latch, missing electronics, floorboard leaks...The only thing I liked was the sideways engine and the 5SPD auto transmission. Either is likely to fail at this point so I left them alone. At least I can work on an AMC when it finally blows up and the longer I continue living with a "professional mechanic" of 60+ years, the far greater chance that has of happening very soon. :/