Matt --

1. You can use dropping resistors to deliver 3 volts, but your load must always draw the same current. If the current demand goes down, voltage goes up and vice versa (Ohm's law at work). And to select the proper resistance value, you must know the load's current requirements. The desired drop across the resistor is 9 volts, so the required resistance will be R=9/I where I is the current.
   

   It would be better to find a 3-volt regulator. A simple regulator can be fabricated using a Zener diode. But you might find your accessory will function at 5 volts, and then you can use a common 5-volt regulator (avaliable at Radio Shack).
   

2. I think you can access the solenoid bolts from underneath using a combo wrench.
   

3. Only one pressurized hole that I know of.
   

   The oil pressure sender used in the turbo 240 cars is a dual device, having two connections. One is for the pressure gauge, the other for the idiot light. If you insist on a T fitting, an industrial supplier will have one. But you're looking at a plumbing kludge. It might be better to run a small copper line up from the tapped hole and connect two senders to it near the firewall.
   

4. T-stat fits only one way (sensor portion into the block), and the bleed hole should be oriented up to allow trapped air to vent.
   

5. Access to the comp board is by removing seven screws around periphery of the PCB. Two of these screws also secure the metal heat sink bracket holding the voltage regulator. PCB comes off the cluster in about 90 seconds.
   

   I was very successful reviving my dead comp board by replacing the LM2902 quad op-amp (the IC) and the transistor.

Don Foster (near Cape Cod, MA)