We had an 8WD WCD last season. The siderails were 1" x 2" x .125" rectangular tubing, and we put the bearings right into the siderails, no bearing blocks. They were designed to use exact C-to-C for #25 chain. Our thinking is that if the chain ever stretched to the point of being a problem, we'd replace it with new un-stretched chain. This served us well through two regionals. We never replaced a chain. Looking back, I think I'd have the students replace the chain at the beginning of each regional just to be safe.
See here for CAD:
http://www.chiefdelphi.com/media/papers/2752