Billfred, I think that people are suggesting that the wheels be mounted to the triangular brackets, with their axes perpendicular to the long edge of the brackets. That allows the robot to be fully supported on its wheels, rather than causing some of the weight to rest on undriven wheels/casters/skids (which would reduce the amount of force that the robot could exert in a pushing match).
Also, why not consider a quadrilateral version of the Kiwi drive? Like what 854, 931 and others used this year? It seems even simpler to build, and a little more powerful (provided that the extra CIM wasn't needed elsewhere).
A note on the kitbot sprocket. I just realized that we ought to be looking for ISO 04 and ISO 06 sprockets, not #25 and #35. They're functionally equivalent to ANSI roller chain sprockets, if I'm not mistaken, but they
do come in 16 mm bore sizes. In fact,
SDP/SI has some, in larger tooth sizes for ISO 04/#25. And
Martin sells a few ISO 06/#35 ones with 16 mm bores. Search
GlobalSpec for "Sprockets, Roller Chain, Metric", for more sources.