if you are tight on space get a batcap 800 they are small and i think with a big battery upfront like a batcap2k or something big upfront big 3 and a batcap 800 in the back u will be fine
what size alt do you have
i am running a zx1500 and zx850.4 and only have a 130amp alt stock, no big 3, duralast gold upfront and stinger spv70 in the back with a run of 1/0 pos and ground from the front the amp voltage only drops to around 12.2 or so the battery is around 12.5-12.7 in the back the front stays 13 or above at idle full tilt