The free exchange of ideas whether in Syn-Aud-Con or FIRST or Boy Scouts, has propelled me further in my field and in life, than anything else. - Al Skierkiewicz [more]
If you do insist on having a machined bellypan, make yours lighter. We shoot to have ours be around 1.5 lbs for an 1/8" thick sheet of 6061 aluminum. I noticed the strand thickness on your bellypan is much thicker than the thickness we usually design for, so you could probably go a lot thinner than you currently do.
Spoiler for A useful tip:
*Note: We design with a total strand thickness between .15" and .17", which when done without forethought could result in warping and loss of torsional strength. Do what works well for your team. Don't just do something because we do it (Central Valley people are crazy ).*
I'm assuming you are choosing to use a custom transmission because it fits your resources better than a COTS one, though if it doesn't I could always lead you to some sources about why COTS transmissions are a great solution.
All that aside it looks like a very promising design that will serve you well should you choose to use it for the 2015 season.