I'll give it a go Scott -
Barndoor buses are pre March '55 I believe. They are most distinguishable by the rear decklid that is hinged at the belt line, resulting in a decklid that is close to 3' tall. Like this:

This is a 15 window barndoor that I would imagine is even more rare amongst barndoor buses. Corner windows make it a 15 instead of an 11 window bus.
I would say the second most noticeable charateristic of a barndoor is the 'lack' of roof overhang in the front. This is how you would tell if a truck were a barndoor, since the bed height is lower than the belt line, they have post barndoor size decklids on them. Notice the lack of roof overhang here compared to the blue bus previously posted:

A
Kombi was a non walk through bus that had rudimentary interior in the front cabin, and nothing in the rear - just plain metal. Sort of like a panel bus with windows and removable rear interior However, seats could be clamped into place in the rear for passengers. This resulted in a combination cargo / passenger bus. Hence the term Kombi.
Samba is just a term used to describe a 23 window deluxe. Hmm, does that make a 21 window bus a 'baby' Samba?
