I did the 4.0 head swap and MPFI upgrade a few years ago, and I can't tell you how pleased I've been with the resulting improvements in performance and reliability.
With all due respect to all the KISS-principle types, I sympathize but consider this to be a most worthwhile concession to electronic technology.
And let me point out that I am an attorney, not a mechanic. I have at best intermediate skills (a lot more now than when I started!) and was able to do this with the help of this forum.
Also, YouTube videos are really helpful in learning how things go together and work.
To save time and hassle I used the HESCO harnes and TPS kit, but if I did it again in future I'd probably just pull a 4.0 flywheel and try to strip down an OEM harness.
You can get anything you need from a good junkyard. Some say the parts are drying up, but you aren't limited to Wranglers; Grand Cherokees have the same parts and there are tons of those in my area.
I'm lucky to have a Chrysler-only lot very near me, but their prices are higher so I've mostly gotten specific parts from there that had to come from a YJ, such as steering column and power brake booster.
Most of the parts for my MPFI upgrade came from a group 93, 94 and & 95 GCs in one you-pull-it yard.
As to HESCO, they really are the experts but they're also proud of their stuff.
For example, their ECM is almost $500 while the yard charged me $27. The only difference is that the HESCO part has some trouble codes disabled so your check engine light doesn't stay lit.
There are a few hinky bits you'll have to search for, such as a speed sensor that has both mechanical and electronic capability.
Mine came from a 91 J10 pickup and cost less than $10.
I could go on all day, but there are tons of threads on this subject around here.
That said, feel free to PM me with specific questions if you need input from a rank amateur who took this on.
"We are all of us in the gutter...
Some of us are looking at the stars."
~ Oscar Wilde via Chrissie Hynde