Do not be overly concerned by the exterior appearance of your CI stack. If they had installed CI indoor plumbing in the pyramids it would still be functioning fine today. What you are seeing is bubbles in the paint on the surface of the CI. It really requires no action but for peace of mind you could knock that scaly material off with a wire brush and paint it black again.

Now the actual pipe from the tee at your kitchen sink is another matter entirely. Before the advent of plastic materials they used galvanized iron pipe to make the 1-1/4" & 1-1/2" fixture arms. Over time the galvanized iron pipe will rust through. If that happens you can cut the galvanized iron pipe off about 1/2" from the CI hub, then using a hammer and punch chisel you can push one side of the remaining galvanized pipe in towards the center of the pipe. As the galvanized is collapsed in on itself that effectively reduces the outside diameter enough that the remaining galvanized pipe can be removed without damaging the threads in the CI hub. One the galvanized is removed you can clean the CI hub threads with a wire brush, the apply pipe dope to the threads of a PVC or ABS male thread adapter and screw it into the hub.

Lazypup, if you're right about those rust bubbles not being a problem, I'll give you a virtual e-hug! Seriously, I've been dreading this job for months!
Your advice for replacing the galvanized branch from the kitchen makes perfect sense.
I REALLY appreciate you taking the time to reply!

Adam

I cannot begin to tell you how flattered I am that you might consider sending me an E-hug, however with deepest regrets I shall have to decline your offer for health reasons. I don't believe my heart could stand such a sudden and dramatic improvement in my sex life.

Hahaha - Alright then, we'll skip the E-hug.
Would you mind if I emailed you a couple pictures of the rust bubbles on the fittings? A couple of those babies are the size of a quarter and protrude over 1/4 inch. I think I just need some more reassurance before I allow myself that figurative sigh of relief.
Thanks,

Adam

By all means feel free to send the pics to me

I received your pictures and have reviewed them.

It appears that at some time in the past the stack was painted with a yellow oil base paint. The bubbling you are seeing is the yellow paint lifting.

From what i can see there is no cause for alarm however if you would like a bit more peace of mind you could use a stiff putty knife and a wire brush to scrap away the loose flaky paint, then repaint the cast iron.