m16 to m4

OK,

so lets say I get a m16 and I want to put on a crane stock, I know I need a buffer tube and such, but would it work for a rifle that started with a full stock or would I need to completely rework the wiring?

Well if you got the kind of stock that holds the battery then I doubt you'd have to re-wire, but maybe re-position them a bit so that it can go into the new stock. You'd also have to get a different kind of battery that will fit in the stock.

Or maybe you could get this but you probably wouldn't be able to use anything more than an 8.4v batt.

that's a possibility, but would I need to put anything on other than a buffer tube, and is it harder than it seems? or am I making this sound much worse than it really is?