I will also post the answer on the IFIrobotics forums page regarding this issue. Look on the ifirobotics web page for a zip file, which will be located at
http://www.ifirobotics.com/kitbot.shtml very shortly. The zip file contains the actual drawings (in PDF format) that were used to make the parts.
The spacer is, indeed, modified schedule 80 pipe. However, you can make it from any material you like.
-Paul
P.S. - I am supposed to put all of my answers on the ifirobotics forum, but this is my one and only deviation from that.