Alternator and voltage regulator recommendation(s) for antique engine based 12V power source
Use a large pulley on the crankshaft to get the altenator speed up-to 2000 RPM or so. Then just use a commodity automotive alternator. (eg from a automotive recycler, or an off-ther shelf aftermarket one)

Most automotive alternators have the regulator built in, but if not regulators can be had from most auto-parts stores.

If this is for a boat, use a brushless alternator.