I was able to locate a fitting and modify it to work. Since the 36 waterpump has 5/8-18 female threads and the capillary nut is 11/16-16, I needed a male x male adapter. The closest I could find was this
https://www.hydraulic-supply.com/ste...852t0608s.html
11/16-16 x 3/4-16 m x m
I machined the 3/4" side to 5/8 and modified the 11/16 side to match the original hose fitting. I also had to drill it 7/16" thru. With that all done, I was able to install my original, unrestored gauge, including the 3 clips for the capillary to radiator support rod. The gauge is reading well and no leaks, so job complete.
Just thought I would share in case someone else is trying to do the same.
Neal