Per section IX, with the size pipe you have (less than NPS1), you do not have to machine one surface flat. It's the second to last sentence in Figure QW-462.3 (a) - General note (b) of ASME Section IX. You just needed to read a little further I think.
Why not oil or polymer-impregnated sintered bronze bearings? You would lean away from the lead and (I think) still avoid PTFE by tuning your impregnation media to the use case.
I second Jessieleo99's comment, and to take it a step further, as mentioned by mrfailure, I would have the bracket/fastener setup tested in a salt fog/salt spray chamber to verify that you are getting the lifespan you want. This way you can look at the whole bracket setup to see if there are...
