My guess those numbers on the waterpump has got something to do with date and model. More important is does your car have the 304 V8 or the in line 6 ( 258 or 232cui)?
My guess is the in line 6. Those waterpump are aslo used in the Jeep inline sixes ( Wrangler 76-79). Jeep parts are readily avialable with B&S parts in Tiel.
Your problem with starting up could be caused by a faulty neutral safety switch and or ( combination) with ignition trouble. A replacement of the neutral safety switch and an adjust of the ignitiontiming will to the trick. You can also use "hotter" sparkplugs and ignitionsystem with an optical contact breaker instead of the rotor.
By the way i think is know your car. Did you buy it in Soest from a guy named Rob? Is it an black matte '78 coupe with wolfrace rims?
Overigens kan ik ook prima Nederlands. Kind regards, David