I've owned a couple of of them (307d and 409d) and I know a fair amount about them. They share blocks with the 616 and 617 but there are lots of other differences between them. For instance, the 84 and 85 have different waterpumps and fan clutches. The fan clutch runs $500. Parts are hard to find in the US. I used to order mine from the UK. I owned the 307d in Europe and the 409d in the USA. I'm of the opinion that they are not the best vehicle in the USA where distances are far greater than in Europe. They are underpowered compared to US vehicles, resulting in a top speed of around 68mph flat out. There are gazillions of them for sale in Europe.
www.mobile.de will turn up hundreds. They can in lots of varieties with 4spds and 5 spds and very rarely automatics. I think they may have built them with the 617 in most years but there are VERY few of these in Europe. Some van converters turbo'd their vans but these are even more rare. 1st gear in 5spd is a granny gear. They tend of have rust problems so I would get a very close look at one before purchase. I can remember seeing one on Ebay in the NE that had more holes than solid panels.