AFAIK, there are at least two. Can't tell you what year or how to id.
One is something like 2.5 turns lock to lock and the other 3 (numbers a guess). Trial and error may be the only way, I couldn't tell you how many turns it is on my own.
P'raps it's the 84-85 "WS6" package vs. whatever they put in the 86-87?
I think you're right though--it's probably easiest just to count the number of turns from lock-to-lock.