Update for all the LS people following along... T56 acquired and installed! Just completed a 700km round trip with the new (old) manual box and the car was flawless.
Also changed the rear diff while I was at it, upgraded to the stronger 1031 diff with the 3.31 rear ratio. Car now cruises really, really well.
For anyone that's also working with the T56 in any project car, I found a couple of handy tips along the way.
There's a reverse lockout solenoid on the RH side of the box, at the top of the shifter. It's massive and created clearance issues in the 240 tunnel, and I wasn't all that keen on cutting and shutting the tunnel. After some searching around on the LS forums, there were a couple of posts about reusing the reverse lockout housing, cutting it, welding it and refitting it into the box.
Hopefully the pictures will tell the story:
Making it so you can slim down the side of the transmission significantly, and also keep the reverse lockout so you don't accidently shift into Reverse when trying to get into 5th.
Also, there's a reverse switch on the side of the transmission as well, and from factory they poke out the trans about an inch, and then add the connector and it's even longer. I found that the T56 that comes in most Fords has a shorter and right angled switch for clearance, so it's an easy swap if you need some extra room on the side of the trans too.
