Cold weather driveability is the issue if it's not working. There are NOS and aftermarket manifolds available.
I have a truck manifold that didn't come with the heat valve. I ran that in the door car until changing out to alternative manifolds that offer no carb heat at all. I don't drive the car much in cold weather. So far it hasn't been an issue, but it doesn't get very cold here, and I don't drive it when the temperature is down.
It's not that it will run poorly once the engine is warmed up. The intake manifold will eventually warm up, but until that time fuel will drop out causing mixture problems.
You should be able to sleeve the bore for the shaft. Once iron has been welded, it can develop cracks. I'd avoid welding if possible. Some folks have had good results doing it, though I'm not one of those people.
CJ
