Just another thought, does your van have a gauge for the oil pressure, or does it just have an oil light? The sending unit for the light is different then the sending unit for the gauge. The light sending unit should just be an on/off switch but the sending unit for the gauge is probably a varied resistance switch. For what you are doing, I would think the sending unit for the light would work better, but not sure how it would work with a gauge, could make it max out.

Yes, install the fittings and tubing for the mechanical oil pressure gauge into the place the sending unit was originally in.

If you want to get fancy, that hole in the block where the sending unit screws into is a 1/8" pipe thread. You can get a short 1/8" pipe nipple (the pipe nipple can be longer or shorter to clear the back of the intake, as needed) with an 1/8" pipe "T" (the pipe "T" can be screwed onto the nipple any way that makes the best clearance) and install both the sending unit, and the mechanical gauge. Use the Teflon tape on all the threaded ends and be sure the pipe and the "T" are tight before installing the sending unit and the fittings for the gauge.