Ha ha, strange. Its rotten. Look at the inside shot you can see through the panel above the tailgate.
Unsure what the last year of Westies in to the uk was...I know you have one, is it a later UK one? I know Malaga was a one year only on 74/75 N reg...then Oxford....but after that was there any others RHD? Given the US markets weren't based on panel vans I suspect that one is just a westy roof on a newer van.
Is yours a RHD van? @Poptop2 was the main archivist....seem to remember that Westies were rare post 74 as competition from uk conversion companies really took off.