Fried Blue Fld wire from Alternator

I would take it right back to the store, and take your multimeter with you. Check the replacement. This is a well known problem on isolated field alternators, AKA either the rebuilder was sloppy and broke or left out the insulators for the brushes, OR THE FIELD itself has a sort to the rotor body. OR they do so on purpose, attempting to sell later units to fit the early applications. This is a dangerous strategy as you just found out.

I WOULD NOT USE a single wire regulator under any conditions. The 70/ later "flat" regulator is far superior.

The blue wire is (obviously) NOT fused, and is simple. It goes back and branches into the "run" circuit coming out of the bulkhead connector, which feeds, depending on year/ model, the ignition ballast, blue field, VR blue IGN terminal, electric choke if used, and a few other doo dads depending.