1)Get a peice of lets say plastic as it is easy to work with and cut it into aa 22 cm diamiter disc. Then drill a hole in the very centre slightly smaller than the shaft. Drill a second hole 10 mm in from the edge of the disc which will connect to the spacer.
2)Get a spacer, an easy way is from a maccano set or something or you could go for a metal standoff, what wvere is easyest for you.http://www.futurlec.com.au/Hardware.jsp
3)For the push rod you could use an acrylic plastic push rod, for ease of use. Drill a hole at the top for the spacer attachment. Also drill a hole at the end of the rod to attach the shaft.
4)For the shaft you can use acrylic again, drill a hole at 1 end.
5)Assemble by, heating the hole on the plastic disc to make the plastic softer so it will harden around the motor shaft. Screw the stand off/spacer on to the disc and the push rod to the standoff/ spacer. On the end of the push rod and the start of the push shaft slide a lose fitting bolt through to allow to for freedom of vertical movment. Slide the shft throught the 2 o rings to directinalise the movment, mount the rig onto a peice of wood or plastic and the you are done.
For the sizes of the hole they depen on the screws you are going to use and what you may have laying around. And for the construction material,plastic may be to weak but it is alot easier to work with.
Apart from that it is alot of trial and error.
If you have any other questions just ask.(and i hope i explained my self well).