the "calibration" of your gauge seemed like it is working fine.
My question, did you attach the resistors to ground at the wire disconnected in the engine bay?
as for the 370 Ohms when cold, was one lead to the engine block OR to the sender hex. there could be some added resistance due to the thread sealant.
I took some guesses at what I though the needle was indicating with your calibrations resistors and put that on the graph. It appears that a couple of the aftermarket senders would work close with that gauge and be "dead on" if using the OEM +10