Here's an update on the waterpump replacement on a 616 engine on a 1983 307d. It is quite unlike the waterpumps on 616's in 240d's. There is a fan clutch with a large bolt which comes out of the back of the clutch with no head of the bolt coming out the front of the clutch. (the fan bolts to the outside of the clutch) This bolt screws directly into the shaft in the center of the water pump after passing through the pulley which is sandwiched between the clutch and pump. The shaft of the pump must be held by a pin of some kind which passes through the top weep hole, through a hole in pump shaft and out the bottom weep hole. The bolt coming out of the fan clutch has two flat sides. These flat sides are matched to a hole in the pulley which also has two flat sides. The only way to remove the bolt is to turn the pulley which by virtue of the flattened sides of the bolt and pulley, turns the bolt out of the pump. The pulley has a piece of quarter inch flat steel welded to the front of it. This steel piece has two flat sides resulting in the necessity of a thin wrench with the capability of being opened to about 3 inches being used to unscrew the pulley. A standard pipe wrench would be ideal if it could fit into the narrow quarter inch space between the fan clutch and the pulley. They won't fit. I ended up using an old british pipe wrench called a footprint wrench to unscrew the pulley. A big set of water pump pliers might also do it but I didn't have any available. It took me quite a while to figure this out and I got some help from a mechanic at a UK Mercedes truck dealer. I was quite puzzled initially by the fact that the bolt that threads into the pump was not visible on the front of the fan clutch. It was only after reaching behind the clutch with my fingers that I was able to feel the flat faces on the front of the pulley to which the wrench must attach.
The system is functional and once understood is not that difficult to work on. However, I have never seen another attachment system like this on any other water pump. Why Mercedes chose such on odd mechanism on a few years production of 616 truck engines is a puzzle to me.