Converting 160 Monza Jr. from 6V magneto to 12V alt/coil/bat

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What all do I need to buy, do, and consider if I want to change the electricals on my '67 160 Monza Jr. from the 6V magneto system to a 12V alternator/coil/battery system?

Also, is there a commonly used, readily available tachometer that I can add to my bike, perhaps one driven off the coil or something like that? I hate to think of getting one of the mechanical bevel-driven setups. They're quite dear on ebay and would prevent me from fitting a gear-gazer.

Thanks,
Brian