I've just come into one of these myself and I'm trying to figure out what year it is. Unfortunately the frame on mine is a bit more beat up, but a lot of the early bits seem to be intact:
- motocross brake levers
- early cantilevers (pre-shimano)
- biplane fork
- Araya rims
- Deer head rear derailleur
etc

but I thought the derailleur would have marked it as a later (of the early) model(s); the brakes and the derailleur seem to be out of whack with each other. Does anyone know the answer? Is there a way of decoding the year from the serial number? I guess the early Stumpys were a bit of a mishmash of parts, but I would like to figure out what is original and what may have been changed later.