line towards the front is the return line and goes to the bottom of the canister.
All the electric senders I've seen screw in and can therfore be removed. If you can't do this, then go to a part/hardware store that has a good selection of brass fittings and find a sutable replacement "T" fitting. the engine block is 1/8" NPT. The cheap aftermarket mechanical gauges typically use a 1/8" NPT w/compression hose fitting. Replace the plastic tubing with brass.
It's definitely best to have the gauge in the pressure line to the filter.
Also, you could try looking in a salvage yard for a 47-59 vintage truck, as they would have a mechanical oil pressure gauge, posibbly other years, and cars too...
