Follow up….after a month delay due to work commitments.
Bottom line: “Soft Flex” brand beading wire in .014” onyx black worked perfectly!
Long story: Lionel “bell cords” are .014” smooth wire, and they fit nicely through the guide pins and holes without much room to spare. I was surprised and happy to find the above beading wire that a couple users suggested, and conveniently it is same diameter. It also has a nice subtle texture caused by the wire braid that is covered in nylon. I paid less than $10 for a 30-ft spool. It took me all of 15 minutes to thread the wire and secure it. I knotted the cab end and tied a knot on the bell end. I secured the bell knot with a tiny dab of super glue on the wire. I left about an inch of excess wire in the cab. That way, when handling the loco if I press on the cord there is some slack, and it is easily taken up by pushing back into the cab. I think it looks perfect. It has some texture reminiscent of tar covered rope, has a slight drape, but is also taut enough to hold shape and not tug on the bell.
Highly recommended solution!