Local hardware store had the parts I needed. The guide rods will be 4mm music wire and the side bolts will be 5mm threaded rods 100mm long. Now that I have the parts, I know what size to make the holes and can complete the design of the components. First designs are done for all the parts except the plunger. I'll print them tomorrow and see how it all fits. Then on to the plunger! I'm planning to use the plastic welding technique recently featured to do some of the assembly, so I'll see how that works also.
Actually, printing depends on FreeCAD producing the stls correctly. This has not been a problem in the past, but I'm using FreeCAD in ways I haven't tried before, so we'll see what happens. In the mean time, here's the outlet piece. See the black circle in the middle of it? That should just be a hole (like the other holes in the shape). That's the part I'm worried about. Will it mesh correctly? Stay tuned!