I spent 8 years in a Catholic seminary in the 1960's, until I ended that career when I discovered the opposite sex. We usually referred to sandals as "water walkers" or sometimes "Jesus boots" - but this was a fairly irreverent seminary that I attended....
Gargoyle's water-walking reference seems to be the appropriate one for the "Grey Funnel Line" reference. Note that the shoes failed when Peter lost faith.
"Shoes of the fisherman" is a term referring to the pope, who is supposed to be successor to St. Peter the fisherman. Jesus appointed his closest disciples (the "12 apostles") to be "fishers of men" (Matthew 4:19 and Mark 1:17). I vaguely remember some pious story about the shoes of Peter. I suppose somebody somewhere found the "actual shoes that Peter wore," assuming Peter wore as many shoes as Imeelda Marcos did. Another thing I learned in my irreverent seminary is that you could build a house with all the slivers of the "true cross" (the cross on which Jesus was crucified).
But from a folk music poerspective, it appears that at one time, "St. Peter's shoes" was a common enough term that it had a meaning that was easily understood - I'm guessing that meaning had something to do with the ability to walk on water.
-Joe Offer-