Most of the Principias that I have seen do not have ground and finished welds, but it appears that the welds are finished in those catalog pages. It doesn't appear that the catalog bikes have replaceable hangers, but some Principias did have them. Pilo models that were used were D50, D87, D111, D115, D116, D124, D175, D210, D297, and others. Principia may have made their own hangers originally though. You might try to contact some Principia owners and ebay sellers and see if you can find similar serial numbers.