[Scott65]

I've used the basic Mad system for over 10 years now. It's been solid. I use a junction on the firewall for most of the engine and interior power, and one on the core support for power to headlight and fan and for a brief time electric water pump relays. I have an ecu that controls fuel and spark, and it's power comes straight from the cut off switch to a dedicated 4 position fuse panel for "clean" power. Pay special attention to your grounding scheme.
ETA: My battery is in the trunk, that's why I say I followed the "basic" Mad system. Some alterations for convenience, and appearance, etc.

ETA#2 I see you mention using the 12si alternator. I don't know your intentions for this vehicle, but if they involve high rpm, check and recheck your pulley ratio. A 10si with its metal fan can be slightly forgiving, the plastic fan on the 12si I've found is NOT. I had one explode, putting the shrapnel through my fiberglass hood. Keep the rpm under 18000 alternator rpms. I've posted about this before. I ended up with a metal fan Powermaster 150 amp, with a larger pulley. It charges fine in all conditions, and the rpms are in a safe place.