I searched and this is all I come up with not my information. “1/2" npt on the water pump, 3/8 npt on the heater hose”.
If I was you, I would run your manifold down to Ace Hardware down 5600 W. in Roy. Take it inside and check the thread size with one of their examples.
GENE WINFIELD HAS GONE TO THE GREAT CAR SHOW IN THE SKY!
jalopyjournal.com/forum/threads/gene-winfield-has-gone-to-the-great-car-show-in-the-sky.1331919/