[sanddrag]

What are the output RPMs at the sprocket on the box? I see that you are gearing down quite a bit initially, but then gearing back up some in high gear. If your goal is to have a fast gearbox with a larger external sprocket and chain reduction, that is just fine. Many gearboxes are done this way. Personally, I like doing all the reduction in the box and going direct drive to the wheels.

As for weight in the plates, you might want to evaluate how much you will get out of them and how much work it will be. I know every last ounce helps, but since they are aluminum, you might not get much out of them at all. If you've got the machines and the time though, some nice CNC pockets could always make it look nice. I'm confident you can still get some weight out of those gear hubs, and instead of holes in the gears, you may want to look into facing them thinner in the center section (between the hubs and the teeth). You should be able to go down to 1/8" thickness safely. I'm guessing the weight savings will be comparable so it is more of a fabrication/style preference.

The shifting dog looks somewhat non-traditional. Is there a reason the "fingers" one one side are in line with the pockets on the other side? I can't support this with any calculations but to me it seems like it would be stronger if the fingers were inline.

Also, I'm curious as to how the dog gears are riding on the shaft. Are you using bearings? If so, what size? If not, are you using bushings or just riding them plain and greased?

Last, what are the tooth counts on all the gears?