ive asked similar questions for my crx project... ive been looking at the aviation world... there are a few companies that offer 35-45 amp alts.(some higher) that weigh in at 4-6lbs
thats shaving some 10lbs off my honda alt... and only losing 20amps output... but im also going minimal on my electronics... my massive stereo system will include: an ipod and plug speakers...
since im running a "lighter" alt the 6lb battery i found will work perfectly for the system also