additional threaded hole?

[shelby987]

I was looking over the built 250 I bought the other day, and I noticed that there is an 'extra' tapped hole that my current 250 doesn't have.....on the back of the engine, right below the pushrod covers, there is one hole on my current 250, right below the last bolt that holds on this cover, on the new one, that same hole is there (believe its where the oil pressure sender threads into)....but there is a second, looks to be larger hole right between the second and third bolt that hold this cover one.....anyone know what its for? I will try to post pics when I get a chance.