Well I dug up a few pictures of the deal going together.
Here are two of the harness I put together to adapt the WRX TCU to the old SVX TCU connectors and the WRX transmission. The entire thing was put together from scratch using just the WRX TCU pigtails, WRX transmission pigtails, and the cluster of three connectors that I desoldered from the original SVX TCU. All of the intermediate wires were done up by me from bulk wire that I bought off of Amazon
Its worth noting that there are six wires (three pairs of two) that are shielded. They are for the three speed sensors and the wiring diagram called for shielding so I figured I would use some shielded pair wire for those ones. I have no clue of its really needed but I figured better safe than sorry with those sensitive signals.
Before I put the tape / wrappers on.
After I put the wrapper on and made things more neat looking.
That long green wire that's apart from the rest of the transmission ones is the MAF wire. I totally forgot to mention it in my original post but the WRX TCU needs to see a MAF signal and if you try and get it from the ECU it will be all wacky and not work right. You have to just run a wire all the way up into the engine bay and splice into the wire where it comes out of the actual sensor. On my SVX the signal wire is white but it could differ.