Well, the glib answer is the biggest one you can fit, but that presents some reality problems that I'll mention later.
I can't give you a direct answer, but can help you figure it out. Your electric (I assume) heater will be the biggest juice-sucker in your list. Each thing you have should have a power consumption (in Watts) listed in the directions somewhere. If you are like me, the directions usually go in the trash with any packing material

Fortunately, there's a lot of good(ish) info on the internet if you know the make & model of each piece. Add up all of the Watts needed to run all of your equipment. Divide that # by 12 (I'm assuming you've converted to 12V with the goodies you want to run) and that will give you the current (in Amps) needed to run it all. Get an alternator that is "one size up." Namely, if you find that you need 57A, don't get a 60A alternator - go for the 100A.
Ok - here's where reality rears its ugly head. The easiest way to think of your electrical system is that your high power stuff runs from your batteries, not your alternator. Your alternator just tops off the batteries when you give them a rest. If you rely on your alternator, you are asking for problems. The other issue is that things like heaters draw more current on startup than when running, so you need to plan for that. The other-other problem is that the wiring harness of the M37, if in excellent condition, is overkill for anything stock (that's good) but might not be able to handle your heater.

If you go for an industrial-sized alternator, you could stall your engine every time you demand high current from it.
I had a buddy that once put a bajillion watts of trail lights on his off-roader. Pretty much covered the front & roof with high power lights. Every time he turned on just the ones on the roof, his engine stalled. He tried to turn them on all at once - only once. Completely fried his battery, which took out his alternator. Left him dead in the middle of rural nowhere.
Don't let all my blathering discourage you - you can hook up all of your toys and more - you just need a system (alternator + batteries) robust enough to handle it. Do a bit of homework about the equipment you have & you'll be able to find something that works without infinite cost or damage.