67 318 running temps in the summer

Your car is a disaster, it will never run right. Call me anytime and I'll trade you for a 69 FormulaS shell, and the numbers matching 340 block. Great project car.
Yes I'm kidding.
I can tell you how to fix it for good, but it will cost you several hundred dollars in parts. It will run so cool, you'll have to put some cardboard in front of the rad with that 160 stat, just to warm it up.

BTW,
I like your car, a lot.
I had a 65 myself back in the Early70s with a 340 in it, Well, it was an early 340 block, with 69 318 everything else. It worked gangbusters until I burned the trans up. I was about 20 at the time.