Hey, Tom. Love your '64. There are a ton of different kinds of headers out there, so it would depend on what kind you are running. Pictures? Now, if you are running exhaust manifolds and the front tab is broken off, that's a different story. I have seen them welded before and a lot of guys have welded cast iron back to functioning condition, but it's hard to do that and make it look like there hasn't been a repair. Also, the thin nature of the cast iron at that point along with the heat/cooling cycles of the part stress it and may cause a crack again.
Personally, I like that you found an old thread and used the 'search community' tab, but I'm not sure if you mean headers or manifolds. The right side one for your car (if it's a manifold), with 4bbl carburetor and the hole for the heat riser tube for the choke, is the toughest one to find, in my experience. At 25 posts (you already have 15), the site lets you post a classified ad for a part you need. Almost there....