616 water pump replacement

[kerry]

I have a Mercedes motorhome(307d) in the UK with a 1984 616 engine. I will be replacing the water pump when I go over in June. According to the parts supplier, this water pump does not have a clutch attached with four bolts like the 240d, or 300d's in the USA but a clutch and pulley that attache with one large center bolt into the shaft of the pump. Has anyone on this board replaced this type of water pump? It requires that a pin, bolt or something be placed through the pump housing at the weep hole and through the pump shaft to hold the shaft while the center bolt is removed.
If anyone is familiar with this arrangement, can you tell me if the center bolt is right or left hand thread, what size the bolt is, and whether there are any secrets to make the replacement of the pump easier. I'm assuming the basic procedure is to remove the fan shroud, put in the pin to hold the shaft (from top or bottom??)unbolt the clutch/pulley, unbolt the pump and reinstall the new one. Since mine is in a van, it looks as if most of the work will have to be done from below due to difficulty of access from above.