1. That's a cast iron throttle body, so a little heat won't hurt it- - - -but soak the idle screw with a good penetrant like PB Blaster or Kroil for several days before you try heat. A slight warm-up with a Propane torch shouldn't damage things if the Kroil doesn't do the job.
2. The hole is a float bowl vent. Leave it open.
3. That plug was installed to block off a drilled hole during manufacturing. The gap doesn't hurt anything.
4. Contact Carb King on this site. His shop has been a Carter-authorized rebuilder since those carbs were new. He can supply that link, I'm pretty sure.
5. The slot is part of the idle and/or distributor vacuum advance system. It's definitely supposed to look that way, only clean. Get rid of the rust carefully, and things should work well.
Here's an old slogan from the 1940's and 50's- - - -"The ABC's of carburetion- - - Always Buy Carter!" Once you get a good-working Carter carb on a stovebolt engine, you'll throw rocks at a Rochester!
Jerry
