Thanks. By now you'd be forgiven for waiting for the audio book.
Hey Ed, a couple of thoughts on your temp gauge/sender/cold running issues:
Does Jake's DTM setup include a thermostat?
Do you have an oil thermostat installed?
I ask because my Beck did the same thing when I bought it. It would barely lift the needle after a half hour of city driving. The only time it reached "operating temperature" was after 10-15 of 3-3500rpm highway driving. Then, ironically, if I pulled a long grade, it would almost overheat. Like you, I suspected a faulty sender of an ohm must-match between the 356 gauge and the VW sender
After a lot of reading in the Samba, I ditched the cheap Chinese shroud which, of course, the builder had omitted the thermostat. Last year I ditched all that and installed a Thing shroud, with thermostat, a Type IV oil cooler, and switched to 30 weight Rotella T2.
Oil is a can of worms and, like the old joke, everyone has an opinion and everybody elses's stinks. Before my mods running several types of multi-weight, my oil pressure light would flicker at 900rpm. After a bunch of reading, I accepted the rational that multi-weight oil wasn't around until the very end of the air cooled vw's life. I know BP is a good oil, I ran Motul 300v 15w-50, which us too. My motor sounded like a box of rocks. With the Rotella, it's smooth as butter.
Best of all, after my mods, my engine warms up twice as fast and the gauge rarely varies from "12o'clock high."