You have an "early" engine in an early production 1987 924S.
Almost certain it came with the "OLD style" water pump. (NOT the updated turbo pump with belt guard)
You can get a belt kit for the early OLD style water pump but if you plan to upgrade to the new style turbo water pump, you need to get a kit that has a waterpump roller that is 46.2mm across.
If you update the pump you also have to cut the rear belt covers for the new pump to fit.
PICTURES:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/774460-early-late-water-pump-question.html
"
SO, IF you do not see the updated white "NOSE"-block off plate on your pump from the engine bay, you probably have the old style pump from the information you gave --61K miles.
BUT since you have to cut the rear belt guard anyway, just take off the front belt guard and check to be absolutely, positively sure.
Then buy the updated pump, the block off plate, the steel belt guard, a set of new water pump bolts, belt and roller kit, some sealant for the gasket-=-black or green I use aviation sealant. (crap to get off but I prevent a "do over") and stuff for the WYAIT items.
EDIT: The engine may not have the updated "Mechanical Belt Tensioner". You also have to get a kit with the correct cam belt tension roller.
GL
J_AZ