RE: Engine numbers
I saw several 39700-- block casting numbers. I didn't see the actual number you listed. Mortec.com has some CSB casting numbers.
I wanted to add, the only CSBblock to have the oil pressure takeoff drilled and tapped at the front of the block is the four-bolt 350. The location is above the timing cover, slightly toward the passenger side.
This other stuff is just general chevy small block, not just 350. If the block has an 8 inch balancer, it was used on trucks and high performance applications. The oil filler pipe in front of the intake manifold was used until 1968. This info came from a chevy small block ID guide. I don't know how accurate?