Is there something wrong with just grabbing all the OEM computers and transmission from an autowrecker?

Quite likely a minefield there. I haven't really looked into it yet.

I do know that the engine and transmission controllers communicate with one another. The engine controller also communicates with the body controller for engine run authorization.

There are eleventy billion computers in today's cars and they are all interconnected in one way or another.

any build pictures, I used a 545rfe with my 6.4 build. i heard they can handle 550-600hp all day

Is the trans up shifted by electrical servos or by hydraulic like the old 727? If elec then why not just use micro switches to up shift and down shift( full manual ). The speed sensor iis inside trans and works with the abs sensors plus main controller. Reason I know the mechanic next door spent two months with the help from the Dodge shop trying to find the problem with a 2011 Charger. The trans would go into limp mode, tried everything, two trans, new sensors, changed tires. Come to find out the previous owner had changed to an SRT8 rear(3.06 ratio) and main controller was programmed for a 2.65, so the sensors couldn't jive and kicked it into limp, even the main engineers from Chrysler couldn't figure this out. Changed back to an original rear and trans worked fine.But chrysler did say the tires had to be within 5% of stock size to work properly(same as changing gear ratio). We think the rear package came with a chip box but was lost with selling the car to dealer to used dealer. As far as using Jeep trans I think they are independent (bolted solid to frame) so no u-joint either, I didn't see the type of slip u-joint you used in your build up pics other than the aluminum piece.
Edit; got the original trans and going to pull it down to see if my idea would work.

Is the trans up shifted by electrical servos or by hydraulic like the old 727? If elec then why not just use micro switches to up shift and down shift( full manual ).

I saw a video of a guy with (probably a GM) transmission he set up like that. Had two (or three?) toggle switches on the dash. For every shift, he had to select the proper orientation up/down, down/down, etc. Every. Single. Shift. No thanks

That being said, it's probably feasible, just not practical.

I just went to the hotwire site and looked at their kit. It says right on their list of what is included/needed that you MUST have the tone rings AND speed sensors from the rear axle installed.
THIS is what I have been telling everyone on every thread I have responded to on two different forums was MY problem! It is EXTREMELY difficult if not damn near IMPOSSIBLE to mount stock tone rings on an 83/4 axle assembly!