I'm reading all of the hate, and this is going to piss off the purists, but....
MOPAR engines are to damned expensive to build, swap, maintain, and, heaven forbid, hot rod. Let's look at swapping into a '53 New Yorker (OK, its a C-Body. but I do B's as well, and it is my current project, so...)....
A turn key LS harness is $100 (e-bay or Amazon. your choice). A pre-programmed LS computer is $199, and that will control the transmission as well. 149 if you send them a core. LS mounts (engine side) are $50 for solid, DirtyDingo mounts. Oh. And around 600 - 1000 for a junkyard drivetrain, complete with accessories (I picked up a Silverado 2WD drivetrain with harness and computer, 82K for $700). And, $120 for a weld in universal tranny mount (again, ebay or Amazon). More for a bolt in - I think its $150.
A turn key Hemi harness is $1100 for the 5.7 or the 6.2. Same price for either. Yes, $1100. If you can find one cheaper that works out of the box, let me know. $600 for the pre-programmed computer OR $350 to program a computer that you send them. $300 for the mounts (Mancini's). AT LEAST $1500 for the engine and tranny from a junkyard. You have to fab a tranny mount from scratch, as no one makes one. BUT, you could probably modify the universal mount above to work with a Chrysler transmission.
All of this goes before the oil pan modification to fit in the older chassis (both engines may or may not need a different oil pan), driveshaft shortening or lengthening and ignoring upgrading brakes and steering, if necessary.
So...why LS over a 5.7 or 6.2 hemi swap? For what a hemi stand alone harness costs, you can do the ENTIRE LS swap. And, because the LS has more support and is cheaper to build, it will spank the hemi on any given day. I get it. I started out to do a 6.2 swap. But it just doesn't math. The car is essentially worthless as a body. A purist will want the 331 hemi that it came with (which is long gone by the PO or the PPO or the PPPO). So, 5.7 or 5.3...it will be worth what it's worth. So, the LS just makes more financial sense and more sense $ to HP. Wish it weren't so. But there it is. Guess that makes me a sociopath, but I'll be a quick sociopath. I'll watch for the red stars....