I found the Torx 55 head/bit easily enough at Napa. The problem was that my cheap sockets kept breaking as I tried to remove the bolts. Bought a new 5/16" hex head for 3/8" socket and it worked like a charm.

I was amazed at how easily the bumper came off after removal of two bolts and four small screws. Even more impressive was the ease with which the bumper slid back on.