Thanks! After days of searching, I found this
guide and this
photo on
Vintage Chevrolet Club of America today. Unfortunately, my 12 volt batt gets in the way, so I'll mount it on the inner fender. The additional volume of water can only help my early 2nd series with no expansion tank.
You are right. It's an accessory, and mostly pre 2nd series. The engineers built in a pseudo overflow tank into the later radiator tanks. I found all this today. It never rains but it pours when it comes to researching obscure accessories. If anyone wants the repro tank they are at
Bowtiebits.com
