A serial number would be helpful, but you really need to get the casting numbers off the heads (take a valve cover off, look around and you'll quickly spot the casting number) and for the block the casting number is at various places like stamped on the front several places. I usually peek down one side near the block drain towards the oil pan and get the three digit code (mine, for example is "880").
Let us know what you find. Are you planning on doing some engine work?
No was not a Vortec from the factory. Vortecs didn't exist in the V8 until 1996.
And counting the intake manifold bolts is the easiest way to tell. 4 per side, and at a straight up and down orientation to the heads. Not angled.
What you will have though is the engine made from 1987-1995, where the center two intake manifold bolts are at a 72 degree angle, as opposed to the others' "90 degree" angle. That means the intake manifold is different from all other small block Chevies made from 1955-1986.
