Greetings!
You're not alone because Pontiac's and Buick's were known as "heaters". I assume that needs no explanation. Unleaded gas is not our friend in this regard. It tends to run hotter (read: allegedly cleaner). I'll assume you have a shroud, have trashed the clutch fab in favor of a REAL GM Flex-fan. Yes, they are available! I trust you DO have a thermostat installed, I've used a 16 lb. 180 unit.
Here's a suggestion that people question but it works! I'll take a wild guess that your Indian heats in one of two circumstances. Either idling (in traffic) and a steady speed or under long term acceleration a long hill. If your vacuum advance is connected like a Pontiac is supposed to, (ported vacuum, more vacuum as the throttle is opened) the former or like a Chevy, (manifold vacuum, when the throttle is closed or at cruising speed) he latter. If you have a lot initial advance, that will make the problem worse. If you forgot to reinstall the afore mentioned restrictions behind the water pump, it'll be harder to control the heating as formerly mentioned. If you have a Carter/Edelbrok carb it's easy as these carbs have both ports on the front of the carb. Install a "T" in the vacuum advance hose. That way your engine is always in some sort of vacuum advance. Reasonably advanced engines tend to run cooler. If you need a picture I can take one if I can figure out how to port it! LOL If you have a Holley, you'll need some imagination, but it's doable as there is a full vacuum port on one of the rear runners of your intake manifold. There you have it.It works for me and I live in So.CAl where it DOES get HOT! Good luck!
