Just to clarify about the gauges....
When you are removing your old motor/trans make sure you label and keep your oil pressure sending unit and coolant temp sending unit wires. They will be put back into the motor. There is a lot you can remove from the OBS engine harness just make sure you know exactly what something is and that you for sure wont be using it before you start cutting. I labeled everything as I unplugged it when I took mine out and it worked great.
For the coolant temp, there is an empty port with a plug in the back of the passenger side head. Use that port and an adapter(or tap and die if you choose but I dont recommend) to screw in your OBS sending unit. The 88-91 gauges take a different coolant temp signal than the LS and if you tap into the LS coolant temp it will give your gauge a bad reading.
For the oil pressure, tap into the oil cooler blockoff plate and screw in your OBS oil pressure sending unit.