I agree with what Jackass_Jack says. Confirm what you have first. There's a few numbers that will help ID what the engine really is. One is the number beside the distributor, which will tell what vehicle the engine originally came in, what trans it was equipped with, and engine size. Depeding on year, it could also give either the model year or Month/Day the engine was assembled. There is also a casting date on the passenger side of the bloace, near where the starter mounts to the bellhousing.
One thing I would like to note, having the aluminum camshaft gear is not necessarily anindicator of a rebuild. for the most part, Truck engines used the aluminum gear as factory equipment instead of the qieter fiber gear found in Passenger engines. Thsi is not an absolute, as I have heard of Truck engines with the fiber gear, due perhaps to a parts shortage.
