As far as I can tell, there is only one (1) port designed to connect your oil pressure gauge/pressure sending unit. See picture attachment below found doing a web search.
On your question about "..what looks like a temperature sensor...", you are correct. It is the original temp sensor for the 292 head. If you look at the snapshot attached below (I took from a picture you posted in the other 292 thread about "vacuum" and "carburetor" issues you have), you can see where your '53 style gauge connection has been plumbed into the thermostat housing elbow instead of using the original 292 head sensor port.
The sensor blocks the port to keep your coolant where it belongs, and you have an alternate temp gauge in use, so not being connected should not be of any concern.
On your low oil pressure description, considering your other thread and descriptions of possible oil blow by and potential significant engine wear, low pressure is most likely another sign of an engine in need of a full rebuild.
Just my 2-cents.
Dan
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
