I will be replacing my generator pulley which has the 3/8 groove with the 5/8 groove pulley which year pulley will work best for my generator. I have bought two new water pumps with the 5/8 groove and both water pumps have the same offset which I wanted so that I can use one belt. The same will be for the crank pulley which year is best to use for this application with the 5/8 groove. Thanks Frenchy
For both the generator & the crank pulleys, '49 Ford passenger car stuff or '48 to '53 Ford truck stuff, all 5/8".
I think 49 Merc pulleys are all wide belt 5/8 inch, so they will work also. If you are running a mechanical fan, you will also need the double sheave 5/8 in. wide crank pulley and the wide belt fan carrier pulley.
Memory is fuzzy, but I believe there are at least two pulley diameters for the wide gen pulley. I would not worry much about it, but the smaller will of course bring gen online at lower RPM.