The GMC water pump doesn't fit anything else and is not being reproduced to my knowledge. There are quite a few military surplus around and the people who have them know they can get a good price for them. I have picked up a few cheap ones that still had the military pulley. The sellers weren't aware that the pump was the same once you press the pulley off. Your chances of finding a cheap way out are pretty slim. Rare parts fetch a good price and you have to be prepared for that when you own a 65 year old vehicle.