Congrats on a '69 convertible. But even more if it is a true HO car. That is really rare. This chart shows the #48 heads as big valve 10.5 compression.Pontiac HeadsThere are many reasons for it to overheat so I would check the basics first.
Original is always best, but, you can use a different carb if it has the right jets and rods inside. I prefer a post 1973 Q-jet because I can convert it to electric choke. Look up your factory carb specs here> Carb specs
If you open the engine, check the cam out for sure. The Wallace Racing site has the cam codes too. And block codes.
I prefer the HEI distributor. No points maintenance, hotter spark. It is a tight fit against the firewall, nothing a small sledge won't correct. You can bench test it by clamping it in a vise and rigging it like it was in a car. Just watch out for the spark. It can reach a foot away and bite like a MF.
