Roy -
Methinks you have (based on the plate VIN 236143257,) a Kombi, which in MOST
cases were delivered to Westfalia for final assembly and conversion.
 However, upon special request from VAG and/or the customer, any of the
models 21, 22, 23, 24 or 25 could be delivered to Westfalia with special
number of windows requested for final assembly.  Myself I would go by the
plate found on your ventilator, because the rear end of your Westy could have
been in a major fender bender resulting in another model's rear being
installed.  STANDARD Microbuses were usually model 22's which came with 3
windows on each side behind the driver's and passeger's door, just like the
Kombi's (23's) which adds even more confusion sometimes.
This is probably in the FAQ URL somewhere, but here's a list of model numbers
and designations for all Type 2's produced thru 1979 as taken from VAG's
listings (The "x" is for the year produced on 65's and later):
Model# - Designation & Remarks
21x  Panel Van, No Side Windows
22x  Microbus, 3 Side Windows, ea side thru 67
23x  Kombi, 3 Side Windows, ea side thru 67 - Often the "source" vehicle for
Westfalia Conversions
24x  Microbus Deluxe, 4 Side Windows ea side thru 67
**Models thru 63 had 2 Corner Windows making it an 18 Window; With Skylights
& Sunroof a 23 Window
**Models 64-67 did not have Corner Windows; Without Skylight Windows makes it
a 15 Window; With Skylight Windows makes it a 21 Window.
25x  Microbus Deluxe, 7 Seater (thru 67 Only - Not used from 68-79).  Window
arrangements in Model 24x apply.
26x  Pickups  (Submodel 261 was a Single Cab, Submodel 265 was a Crew Cab
Pickup)
27x  Ambulances
I might add that in the 20 years of producing window rubber kits for
"splitties" I have (to date) found over 250 different window arrangements
regardless of the base model which is dependent on the number of stationary
side windows, popout windows and skylight windows.  Example - you could order
a 22x Microbus, have an extra window installed and possible the skylight
windows installed optionally either by special order or at the dealer in some
cases.  Itsa real nightmare when someone calls for a "kit" to restore all of
the window rubber on a "splittie" - ya never seem to find any consistency on
the base model reported, hence that is why I do not have "kits" -
everything's sold separately to reduce "cornfusion".