1990 Suburban 4x4, TH400 to 4L80e swap

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Hello all,

First of all, I am in Europe/Bulgaria and I do not have easy access to junk yards and spare parts for USA cars.

I am planning to swap TH400 with 4L80e in my 1990 Suburban 4x4.
Engine is SBC 350, TBI, which I will also inspect and rebuild as necessary. Transfer case is NP 241C.

What I know so far is that I will need at least the following (random order):
1. TH 4L80e to NP241C transfer case adapter (GM Part 15724745).
2. Stand-alone transmission controller (I may go with US Shift Quick 4 Gen2).
3. New cooler lines and bigger radiator.
4. New transmission mount and to relocate cross member.
5. New transmission dipstick.
6. Adjust driveshafts, front and rear.
7. Adjust shift linkages for transmission and transfer case.

What I do not know and need info and help about are:

1. Do I need new flax plate for this engine and torque converter combo?

2. I have read somewhere that 4WD 4L80e have only one speed sensor, but in this swap to fully work, it needs two speed sensors. Is that true?

3. TH 4L80e transmission itself. Here I have two options:

3.1 Buy rebuild TH 4L80e from USA (I have some places in mind, will discus this later).

3.2 Buy “rebuild” TH 4L80e from an individual here. As far as know the story, he order it for his H1 6,2 Diesel but never install it.(He is reach guy, changing vehicle often, so, I would believe this story). It sits abandoned for 10 years in his garage. It looks clean. The code on transmission is 8KYP on front label, and KYP on yellow rear label. Unfortunately, there might be some water penetrated in it. There was leaking rain pipe near it and there was water in the transmission transport box. Isn’t it too risky?


Thanks a lot for any info, advises and help,
Ivo