Only place I can envision a leak that would spray all over the place like you describe is the timing chain cover.
My experience building small block Chevys is limited to vinatages from the mid 60's, but I believe the T.C. cover has remained the same into the 80's.
As i recall, there is a rubber wick of sorts at the very bottom of the cover that sits in a groove which kind of hooks onto the oil pan.
If this rubber is deteriorated, logic tell me it would leak (more) when very hot. A relatively small leak in this location combined with the air flow of the fan could certain blow a lot of oil onto the ground, and you would have a tough time actually seeing where the leak is with engine off & cool.

David