The way to tell if it is the early, block is that the distributor hole goes right up to the top of the intake manifold sealing rail.
If yoy want to tell the difference between a Mex block and a USA block the easy wak is to look at the rear where the bellhousing bolts on... On a USA block the bolt bosses are blind the casting extends right back to the water jacket wall. On a Mex block the holes are open, you can see light out the other end.

Also do you know how to read casting dates ? And where they are located ?