69 C10 396 Coolant leak behind the engine

[1SG.Rob]

First time poster here. 2 days ago I lucked into the C/10 that I've been looking for since I can remember. Only 75k miles and has been covered in a garage since 1990. I knew when I bought it the rubber parts would all need to be replaced soon. Yesterday it started leaking coolant and I assumed it was the hoses. Upon closer inspection I saw that it's coming from the rear of the engine on the passenger side. I can't get in close enough to see it directly, but I am guessing it is the intake manifold gasket or maybe even head gasket. Does this make sense to you guys? It only leaks when the engine is running and has warmed up a bit. I won't be able to get it on a rack until next week to take a closer look. Any advice or tips would be most appreciated. My apologies if this has been posted before.