To get a top panel without mounting hardware visible (easily at least), I would use two top plates. The first would be basically identical to the stock top plate with the exception of having countersunk screw holes for all the chassis hardware.
The second top plate would mount on top of the first, using items like the power transformer, potentiometers, RCA jacks, speaker posts, etc. to clamp the two together.
You can do a bent panel for the FP-III, but it's worth considering what the rest of the chassis will look like first. For some of my own projects, I have just used two individual plates mounted together at a 90 degree angle.
-PB