I'm about to go onto water pump #4 since I bought this car and I'm considering instead of the cheap cast Gates/Carter pumps an AC Delco 252-629 which is aluminum but I trust their bearings not to fail after a year and a half.
Problem is that the outlet port for the heater core isn't included in the casting. Instead you get a threaded hole. Me, the parts house and every plumbing supply house I've tried so far cannot find a fitting to go from the 5/8" (or something similar) port to the 3/4" hose. How on earth were they expecting you to use this pump with a heater core??
That's definitely strange. Also surprising no stores have something that will work. Maybe try a place that works with hydraulic lines.
Try the aluminum GMB/MasterPro 110-1030 listed on RockAuto.
The one I purchased from them was made in Japan, which I'd trust for quality better than even some US-made parts.
('83 258 w/V-belts)
Good luck!
David
Can you find a fitting like this, that will allow you to go from the hole in the water pump to a 5/8" hose:
https://www.speedwaymotors.com/Short-Chrome-Heater-Hose-Fitting-5-8-Inch-Hose,878.html?utm_medium=referral&utm_source=share&utm_campaign=share&utm_content=ccc0211b-61f0-46e3-8c38-73327aacc663
And then one of these 5/8 to 3/4 hose adaptors?
https://www.summitracing.com/parts/uac-hf1907c?rrec=true
May not be the prettiest or most elegant solution but it could work
Good luck!