Nice work. I like it. You may want to make it smaller though. There is a lot of "empty space" on the bottom plate. If you can remove that from the bottom [and top] you should be able to lose a few ounces. Also have you considered milling out the middle ring that attaches the speed controlers and spikes? We did this last year [something VERY similar] and it will save you weight but only if you have access to a mill. Also you might want plot out where your holes will be on Inventor and punch them, and then mill out large triangles to save some more weight. This can also be done on top.
Check out these links for more information and if you have any questions let me know. I'll try to post a picture or two of our middle ring that lets us put our speed controllers back to back.
http://www.chiefdelphi.com/media/photos/28671
http://www.chiefdelphi.com/media/photos/28627
Pavan.