seeing as I just did this, the problem youre gonna run into is youre body isnt made to support the buffer tube rear wire, youll have to saw off all but 1inch of the stock nub on your body, then dremmel a path for your wires, now im not sure of the sr series wire sets, but my original wire set wasnt made to go through a buffer tube, so youre gonna want to get a wire set that doesnt have a tamiya plug immediately after the exit the body, so the wires will flow into the tube, from there the only battery that fits in the tube is 11.1 1200mah, now the firefox battery sticks out of the tube like a 1/2 inch, but the kings and hot power batteries fit nicely, im unsure of how the firefoxs protrusion affects your stock collapsibility. used these for my external parts:
buffer tube:
http://shop.ehobbyasia.com/accessories/stocks/aeg/element-lithium-battery-stock-pipe-for-m4-aeg.htmlI highly reccomend over the king arms because this tube has a port cut out on the side for wire/ plugs
stock:
http://shop.ehobbyasia.com/accessories/stocks/aeg/ares-vltor-clubfoot-mod-stock-black.htmlnext time im out youll see this set up in action

*burst*
