I didnt do a manual swap but as for some of your questions:
gauges: Yes get an adapter for the factory oil pressure gauge, and on the coolant temp when I first done my swap I used the 3 wire unit but was told it wasn't as accurate with the obs gauges so I tapped my water pump and put in the factory one for my truck. But my gauge reads the same as the 3 wire unit did.
Pcm: I removed my 92 ecm as its not needed. you only need the one for the ls1.
Radiator: Yes you can use your stock one. I swapped mine to 1 ton rad and installed the 05+ efans.
And the vss in the t56 is the only one you need you dont need the one out of the getrag. as the t56 one is going to be the right one for the pcm.
Hope this makes sense.