I am now using an ACE stock with a 11.1V 1200mAH Firefox 3-cell LiPo battery. Fits like a dream. Although some dremmelling was required to run the wires from the rear of the receiver in through the "buffer tube" of the stock.
Here is a pic of the ACE Stock :
I'm almost done this custom gun project, so I'll post some pics (tonight) in the Airsoft Media section of ASC here, and on my site (
www.6mm-mag.com).