'78 K10 Mystery Oil Leak

[RyanAK]

Brought the truck out of town for work the last two weeks for a little shake down... and because I'm bored to tears in the hotel after work and thought I'd do some small projects in the parking lot.

Rig is a '78 K10 Suburban Silverado with a GM Crate 350, TH350/NP203, 3.73 gears. Crate 350 was put in by a PO and only has ~4,000 miles on it.

Other than the vibrations I'm chasing at 45-55 and 65-70 mph, the truck is pretty darn comfortable and seems reliable.

I have an oil leak that's wetting down the starter pretty good... and since this is a GM crate 350 that supposedly has a place for a dip stick on both sides of the block, I suspect that the passenger side dip stick hole is open and the cause of the leak. The last spark plug gets a bit wet, and the rear of the exhaust manifold. But mostly its running down the back of the block, bell housing and starter. Oil and trans pans are slick. Ditto frame and front drive shaft. Ya think I'd be able to see the passenger-side hole to verify and make a plan to plug it. Nope. More effort needed.

I gently snugged down the valve cover since that was my first suspect. I'm fairly convinced it isn't leaking. No evidence around intake manifold or distributor either.

Anyone know precisely where the dip stick hole is on these and how best to get to it? I'm not losing much oil... maybe a pint in 700 miles... but it's a right mess that's definitely annoying.

Appreciate any guidance. Thanks, fellas!

Good grief. Old trucks.