I was recently commissioned to paint a Battle Core Optimus into MP-10G colors. I also scratchbuilt a proton Pack that can be attached in both modes. It's made from styrene, a little bit of Lego, some twisty ties and random bits from my model parts bin Enjoy a full gallery here: Customs By Spoonman
Damn that’s pretty cool. And a good choice to use too, considering it was the proper colors to begin with! Did you keep the combining parts intact?