Howzit!
We started using WCD last year and really like the performance. So unless the game dictates otherwise we will be using it again, though possibly a hex frame 8 wheel WCD.. I posted earlier
..
A few things.. Top render has the transmission constrained on the wrong side of the drive rail.
You will be better off not using the versa blocks on the center and just drilling your center hole to use the WCD gearing block.
http://www.wcproducts.net/217-3634/
You will also need to drill a few holes on the drive rail for the bolt heads on the transmission plate to nest into. This will allow the transmission plate to rest against the drive rail giving much better support. You can run a dual sprocket on the transmission to drive each of the outer wheels.
I suggest #35 chain. We have been using #25 but last year we had to tension the chain more often due to our use of the WCD 3 CIM dual speed transmission. (great transmission by the way)
Also factor in a chain/belt cover. Nothing is worse than an electrical wire getting in there. Most of the time an encoder is mounted to one of the outer wheel shafts. Plus the judges like things to be safe!
I am sure I will think of more after I post this..
Good luck with this, looking good!
Aloha