Hey,
I somewhat successfully used those V-bearings on angle iron, so did Benny (Ynneb). It is on my third machine, first being a JGRO, second was a torsion box – skate bearing machine. It works quite well and is a magnitude cheaper than using the proper rails. My machine is a 24” X 48” and mostly wood. If you can figure out how to support the angle iron for the length you have in mind, you might want to give it a thought. You can see my build at:
http://www.cnczone.com/forums/showthread.php?t=15270
You can see Benny’s larger metal machine at:
http://www.cnczone.com/forums/showthread.php?t=6143
My recommendations: start a bit smaller until you get the hang of this. Large machines are a PITA to build and costs get large very quickly. You can always build a second machine and re-use many of the components. Chain drive seems scary to me (too loose).
Steve