I agree.For a NOS gauge, that gauge looks a bit odd. Hopefully it is for a 56 Chevy.
Before tearing anything apart, I'd wire up the gauge and sending unit to a battery, and suspend the sending unit it a pot of water on the stove. By monitoring the position of the needle versus a good thermometer in the water, you'll know if it reads accurately. See my testing of sending units at 1956 versus 1957 temperature sending units .
Also also, before you tear anything apart - one of the guys on that thread reported getting good results with a stock '56 gauge using the Wells TU4 sending unit, which he bought from AutoZone.