You could just look at it for the molded in manufacturing date code like
the one Neil linked to. It will have the calender year stamped into the
center of a ring of dots. Look on the top section in the area that would
be beneath the ashtray.

The side vent version can be easily determined from looking at the side
hose holes. A 2.5" round hole near the cold air intake for 82-86 boxes,
for cold air dash end vents. Oval side hose hole near the dash face for
87-91 with heated air available at the dash air vents. (early still 87
had the older round cold setup, most 87 have the newer)

Many later boxes had bot sets of large side holes but one set is plugged.

Mark

Jim Felder wrote:
>...............
> It could be from an 86 I bought parted out, my old 1990 Carat, or my
> daughter's 1991 GL that had a bad motor and I swapped the good one out of
> this into it (I think).
>
> I have gotten some pretty good tips on whether it will work or not in an
> 86, I just need to follow up on the replies I received and figure it out.
> It's going in one of John Rodger's vans, and by the time it is done he will
> know where I live, so it has to be right!
>
> Jim
>
>