Most from that era will likely be a 4 speed Spicer manual with a granny low. There were a few automatics running around back then, but not many. It's been my experience that the manufacturer of the incomplete chassis the bus was built on would have been able to tell you just about anything about the chassis and running gear from the incomplete chassis VIN, however, 1983 goes beyond what most are able to look up these days. Most usually can't look up anything older than about 10 to 15 years back.
As for the engine, CK is right. Another way of identifying the engine in lieu of a tag (some go missing over the years) is casting numbers on engine block, intake manifold or heads.
Most skoolies built back then were nothing more than incomplete Class 7 truck chassis outfitted by the coach work company, and most back then were gassers. With the exception of the Detroit 8.2 diesel, most chassis manufacturers of the time used their own gas V-8s. A good start in getting some help here would be to mention whether this is a Ford, Chevy, International, etc. (Ford Bx00, Chevy Cx0, International Sxx00). Many of the buses from this era will still have the badge on the cowl. Knowing some of the basics will help in finding where to look for identifying information.
"Cheese Wagon" <email@example.com>
Former owner - 1989 Ford B700 64-pass Blue Bird (Rest In Peace, Cheese Wagon)