Can't help you with part numbers, but take a look at the attached section of the Carter TQ Service Manual. If you want the full PDF you can grab it HERE.

In fact, I've got a couple more things sitting on my Web server, so check these out:

1) 1972 TQ Mopar Reference Booklet

2) 1982 TQ Mopar Reference Booklet

There were two types of idle mix screws used, and while it does NOT spell out the details and/or differences for the '71-only air circuit, one could expect this to be a reasonable assumption. Further on, when you successfuly extract what's stuck in there right now you'll be able to measure this.