Yes I think it will be ok on 48V. If it is a low wind area , you will do better with a smaller prop. I n a good wind area the original prop may be ok.
Those low voltage generators rarely fail unless rust has pushed into the copper. Give it a wash out in gasoline, let it dry and if the resistance between shaft and winding is over 20k give it a try. If it works, give it a coat of air drying varnish. Take a good look at comm and and brushes, bruses should be free in holders and have reasonable pressure, comm should be concentric with mica below the copper bars.
If the comm needs attention,read up a decent book on the subject, it is a critical,process and would wast a lot of time here describing it. if you get to the point where it will motor but not generate , suspect the comm for high Micas or shorts between bars.
flux