Thanks for the additional photos ... now that I look at that tap tool, I think I actually have one, at least it looks very similar to the one that goes with my easy-out kit.
I'm trying to make my shopping decisions on egauges, and I noticed they have a "floating ground" sender available (you can buy the gauge and sender separately). Do you think that might be a good idea, since I can then use teflon tape without interfering with the ground? It would add another wire to the mix, but would maybe allow a tighter connection between the sensor and housing lid? My biggest fear with the whole project would be having the sender loosen and oil shoot out the top of the housing while I'm driving down the highway.
I think I'm going with this gauge: http://www.egauges.com/vdo_mult3.asp?Type=Elec_Engine_Pressure&Series=Vision_Chrome&Units=E. My boost gauge is the Vision Chrome series as well (though I don't think I can mount them close to reach other, I really don't want to hack up the custom wood piece I made for the boost gauge!).

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)