90 was when they crossed over to 4x4 so I beleive some would have had green tops but in sure others will verify!!

Sounds like a syncro worn on the box side of things.

Vin number just make sure the chassis plate by the drivers door matches the vin plate and log book.

If it's the original engine the number will be stamped on the block on the side but not the end of the world if different as a lot would have had a new engine at some point.

Main thing is good history with cossie's, as then at least you know it has been looked after over the years.
Also check for rust in the usual places ie arches and chassis rails etc