troubled carter 2bbl. what else were they fitted to?

Unless it's broken or complete worn out, I'd clean it out and put a kit in it. If it's the car in your avatar, that was the last year for the clamp-on style air cleaner so, anything you find, will be the same year or older. You might luck out and find an NOS one but I wouldn't count on it. The MPH limit is not usually a carb problem unless the float valve is partially plugged or stuck. I would check the fuel volume, and distributor for more likely causes. Even a plugged exhaust is more likely than the carb.