https://www.clevelandpap.com/product-category/engine-packages/

seems like they pull everything from a car and and show it running on the pallet.

seems like a good deal and "might" make it easier to do a swap into an older car. less of course the cutting to make the trans fit.

If I had a spare $8700 I would drive down and check out the 6.4 if it had a 6 speed and jump on it if it all looks good.

I purchased an '06 6.1 hemi and transmission pallet from them. No complaints from me on the products delivered or the service provided.

how hard was it to adapt?

Not too bad.
Here is a link to some of my build
https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2147353/2.html

Originally intended to use / modify the factory wiring harness, but upon looking at the 40 lbs. Of wiring I decided to go with a hotwire harness. I sent them my computers, shifter, gas pedal, etc and $1800 dollars.
I used the tone wheel kit to supply wheel speed to the computers, and bought an adapter flange from the driveshaft shop to deal with the flange one the nag1 transmission. I only have a few dozen miles on it at its point, but it seems to work.
The custom headers, and my overkill fuel system cost me nearly as much as the engine/transmission pallet.

Bought a few long blocks and bare blocks from them, well described and always helpful only ever had an issue once, it was a shipping issues and they bent over backwards making it right.

Thanks.