Gs 160 12v upgrade

Hi, I was thinking of upgrading the ignition on my Mk1GS 160 to the vespatronic system, can anyone sugest what battery I should go for and what other parts I need to buy. I have looked into this a bit and have conficting views on the wiring loom, brake light and ignition switch. Thanks Andy.

Could someone from Sip please reply, I have a £500+ order for you sitting on my notepad and a GS in the garage waiting to be assembled, Thanks Andy