340 Motor with 360 heads?

The balancer has stock drill marks, it's fine.
The intake gasket is fine. That upsidedown "U" shape is OK to be seen like that.
Early 273's and 340's are the only engine to come stock with mechanical pushrods that you have.

The casting number may also be under the head where the 2 center runners meet by the intake. Once you remove the head, you'll see them.