Just so you know Mike, the Mystery Machine from the live action movies is in the Barris Collection Museum...you can probably see it online, I believe there is a website for the collection.
It is just a normal American made Chevy Van. (C10 or C20 I think, doesn't look like an extended or C30/1 ton)
I'm not sure where you found a Bedford Mystery Machine? although there are many fans around the world who have created their own versions of Mystery Machines,
but a Bedford is an English Utility Van (made by Vauxhaul I believe) and not the van used in the movies.
oh!...I just found this! This says its a pic from the Barris Museum:
AND....
HERES a cool home made Mystery Machine I thought you might like.
This one is interesting because its just about the closest thing to the cartoon version.
Its originally a '68 Chevy Van short wheel base which has a similar kind of shape.
I'm not sure how accurate the interior is though! lol