For the OP: I'd absolutely get it professionally welded. Anything that spins at high RPM or houses something that does should be handled with at least some degree of precision, and I really feel like having your alternator turn into a grenade inside your engine is not something you should consider as an acceptable risk.
As to alternator vs generator: Technically, an alternator is a generator, but the electrical device we commonly call a "generator" (or Dynamo) spins the wire windings around a fixed magnetic field, generating 100% of possible output all the times. An alternator spins the magnetic field within fixed wire windings. I can't 100% remember the construction of my CE Niehoff 200A, but I remember the characteristic of how it operates: the higher the current load demand, the harder the engine has to work to turn that device. The variable output of the devices indicates to me that it would actually be an alternator. Another sign of this is that it uses a discreet voltage regulator, which is a component necessary for providing a field current to trigger the alternator to actually generate current. It's very common of the military to give a device its most general name possible, so the fact that NSN 2920014209968 points to being a "generator" really doesn't surprise me, but I'm fairly confident it's actually some form of alternator.