Since you are locking the ignition, could you use one of the MSD starter savers or even the MSD adjustable timing control to start the car? I think the starter savers will let you choose between 10 or 20 degrees of retard, and the timing controller will let you select any value between 1-15 degrees. Could be an easy fix.

As for the 16 Volt battery, is it simply a drop in or do you have to change or protect any other electronics? I saw the tip about not charging and running the water pump at the same time. Sounds like if you run an alternator you need to go to one that will charge a 16 volt battery. Also sounds like you need a charger that will charge a 16V as well. What other watch outs are there?

I just rewired my car, replaced the starter, and set it up for two batteries in the trunk. I hate having to add the weight even though it is in the rear. I am not running an alternator but considering going to one, (more weight also). Sounds like a 16V battery, and alternator are the way to go. Probably less weight at the end of the day. Just want to make sure it will not require a lot of other changes.