TCU = Transmission Control Unit. It will be easiest if you have a compleat donor vehicle to work from, because you'll need the transmission, TCU, transmission wiring harness, and sundry other little goodies.
Also, if you currently have a manual (likely a damn Peugeot...) you'll need to change the TPS - since the auto version for 1987-1990 is actually two sensors in one case - one reports to the ECM for fuel metering, and the other reports to the TCU for shift point and load determination. All other RENIX sensors are the same - they're just for engine management.
I don't see a lot of reason why you could not use a later AW4 - but do get the transfer case with it, since the output spline count changed from 21 spline to 23 spline in 1989 or 1990 (I don't exactly recall,) and your early transfer case won't bolt up to a later transmission. The rest of the drivetrain is the same.
And, remove the Grille Opening Panel (not the grille itself - but the part that the grille and headlamp buckets bolt to) to get yourself more room to pull the engine. There's little enough (looking longwise) as it is...
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