Honestly, I didn't think I would ever ask for help on such a simple issue as a tack replacement. Until I got my hands on some parts, and mixed in is what I believe might be MTH parts with Lionel - that's my best guess. So to the question, what kind of tack would be used on the armature on the left? The one on the right I am quite certain is Lionel.
Here's a closer view of the one on the left
Thanks! George