Thanks Wendell for doing the legwork on this. I was able to order from Watts the LGB 63218 loco pick-up shoes to fit my Porter.
They are made by Massoth and the new part number is 8313104. The four-pack cost $13.95.
The old "skates" had worn through like Swiss cheese and were snagging on rail joints. The loco's bottom plate was held on by four screws and it was an easy swap. The Porter runs great now.