I have searched the internet for information on how to replace the drain mechanism. The tub is circa 1955 and has a lever that rotates to lift and lower the drain. Looks like it consists of a multi-piece rod assembly that I can't seem to get out. I haven't seem any diagrams or sketchs that depict my type of drain.

Squirt some WD40 down there and put a little muscle into pulling it out, Good luck, Tom