Ken, i made this setup this weekend to build a wing for my Brodak Shoestring. I made a tool to cut the holes in the ribs with a piece of 3/8" od copper tubeing with a 5/16" drill bit inside of it for a guide. I filed teeth onto the tubeing then inserted the drill bit into the existing 5/16" holes that were allready in the ribs. I inserted the drill bit end into the holes in the ribs and turned the tubeing by hand & it expanded the holes perfectly to 3/8" dia for me. I expanded the holes because i like you wanted the guide rods to be stiffer and not sag. I had 3/8" solid rod easily available to me and used angle iron on the ends to support the rods. I held the rods from moveing with end blocks i drilled & tapped & used 1/4-20 bolts to hold the rods. A C clamp on one end kept everything from moveing....Gene