I see you already bought a new Balmar 100-amp. Nice work. Here's my 2-cents anyways...
I modified two Leece Neville 105-amp alternators to accept external regulation. They worked great for a while, but then the external regulator stopped working (made by ample power NOW OUT OF BUSINESS - POS). I got them back on their internal regulators for the time being. On average these alternators seem to put out about 130 amps together at low-medium RPM. I could probably get a little more juice (and prevent battery overcharging) if I shelled out a boat dollar for two new balmar external regulators and a centerfielder. The problem with Balmar is they are freaking expensive for what you get (my Leece Nevilles were a buck-fidy each on eBay vs 600 for Balmar). The good thing about modifying an alternator to accept external regulation is that you have a backup regulator if they fail.
Surprisingly, alternator shops have not yet been replaced by online stores. Stop by your neighborhood alternator shop, bring your current alternator, and tell them what you're looking for. They might have something for you, or at least some advice. When I bought my Leece-Nevilles online, it was a huge headache to get the right size pulley. After failing online, I walked into a shop, brought the alternator, and they hooked me up immediately. As a side note, they also said Leece Neville makes a great alternator.
Whatever you end up going with, you'll minimize headaches if you stick with a single belt-driven, small-case alternator. This means you'll have to get something rated at a maximum of about 100 amps. Balmar makes a 100-amp which would be a direct replacement for what you have. Externally regulated, you'll get about 150 amps of charging power, about accurate for a 600-Ah battery bank. Even for my bank of 750Ah with 130-amp charging power, if I drive for a couple hours each day (like 3), I don't have to run the generator.
For batteries: 6 golf cart batteries fit in a footprint just a little bit larger than the 2-8D batteries I had in there. Try the Full River DC224-6; they're a great value. They are AGM batteries, so can accept charge faster and are sealed (my last batteries leaked, dissolved the tray, and got on some electrical wiring which sucked). Because these batteries are 6 volts, you'll wire each pair in series then the 3 units in parallel. They work great.