Was a PA/PB one i bought it a few months ago from Martin, tried to get another from him but he said he has only the Space Van ones left. I take it Space Van ones will not fit on a PB?
the PB ones fit on to the filler pipe which sticks out of the van. On a space van the filler tube is flush with the body and the filler hole is bigger.
I did order one from ebay, it was advertised as a "vintage petrol cap" and looked similar and the mesurements seemed about right but turned out to be about a mm off [V]
i will have a look tomorrow for you in my collection of goodies. as i think i remember seeing one a few weeks ago. i will let you know if i have one asap.