Most automotive alternators will develop 60 - 90+ volts when open circuited - ie. not connected to a battery. (A battery acts as a stabilizing ballast to the alternator output).
Presuming you can locate a suitable regulator, a Delco probably CAN successfully charge a 48 volt system. Issue is whether the rectifier diodes will hold up working at this higher voltage (they probably will). More problematic is whether the field/stator windings' insulation can withstand the greater "I squared R" heating losses that will be developed.
I'd suggest starting with a 24 volt Delco (plenty of them on Ebay), apply a custom-built regulator to it and see what you get.
Not certain why many wind turbines use permanent magnet fields. I suspect it's for efficiency (no energy lost energizing field windings) and better low RPM performance. The downside is regulating a PM field alternator is more difficult/expensive.