I am working on my own Lowrider V2 build and made an extra set of flat parts. They are made of 3/4" MDF and created as per the specifications on the Thing-A-Verse page. They are the 25.4 - 1" size. If you are interested please feel free to send me an email: firstname.lastname@example.org
After making them I assembled the printed parts on them to ensure placement of holes were accurate. Please note that these are made of 3/4" MDF so if you are building your machine from the kit you will need to use longer #6-32 hardware.