66 Barracuda 273 Intake Manifold options?

Looks like you have the A/C version of the thermostat cover and radiator hose. Just an observation, it should still seal and work. I tend to like the stock non-A/C cast iron cover myself. Back to the subject, I found a sealer that works great on leak prone covers. If anyone has chased one on a PT Cruiser, you know what I mean. I found a tube of a sealer made specifically for sealing thermostat covers and water pumps....I believe it is made by Permatex....I can't seem to put my hand on it at the moment. Anyway, that did the trick and I haven't had a leak since. I've also used it on those leak-prone chromed thermostat covers with good results. If I run across that sealer, I'll update this post.