One sure fire way to tell a 3A frame is the offset motor mount location and the lack of separate bumper gussets.
Measure your wheelhouses to decide if the tub is 2 or 3.
All the other details can help narrow down the year.
It is getting so there are a lot of salad jeeps built from piles of parts from several different jeeps so you might not be able to narrow it down, especially if you have a mixed 2A tub on a 3A frame or vice versa. Some guys will build a jeep, then buy a data plate and call it whatever the data plate says it is, and title it using the totally unrelated data plate. If you have one of these, just enjoy it and try to figure out the individual parts as you work on them and need replacement stuff.
And all the jeeps I have dated followed me home, so be careful with the dating thing.
