Summit Racing oil

I'd love to see a picture of the labels and date code on that GT 50.
Do you mean the Pennzoil 50 wt? It is AT LEAST 20 years old, fresh as the day it was made, and both cases were a gift from a friend, who retired his twin 454 powered 100mph ski boat. (He won ski races from Catalina to Long Beach, but got old, and had too many broken bones to continue....)