Which style alternator do I need?

Man thats some great information! I really appreciate you taking the time to be so detailed in your descriptions. When I ordered the repo under hood harness, I ordered it with electronic ignition, and it does have the two plugs for the double field alternator, so a square back is what I need. Any Ideas on how much amperage and what brand of chrome atlernator is best? Ive seen alts listed at 100 or more amps, how much is too much?
Thanks,
Martin