That sender sticking out of the case towards the distributor is the oil pressure sender. It turns the idiot light on and off in the tach gauge.
Many of us run a "T" out of the case at that point, then attach both temp and pressure senders there. Yours works just as well at the dipstick.
Six of one, Half dozen of the other....
For a more detailed explanation of the gauge info, thou shalt consult "The Holy Book of Annunciators".