How does one identify the amperage or output of an alternator?

Are there part numbers or anything visual I can check? Check for ohm or resistance across certain terminals?

I searched around here and Google for a bit and came up empty handed.

I have a couple of dual field alternators laying around and figured it would be a free upgrade to my Valiant since I have them already. One came off a 1973 motorhome 440 and the other a late 80's Dodge truck.

either one could it be nice. I think a Motorhome can't get ever an small alt. The best you can do is take it to a test to a shop.

PNs are usefull BUT just if comes from tag if still present. Housing PNs are the same to several alts. The big diff its on the stator being wider and smaller gauge windings to fit more, but they don't have a PN

HOWEVER, I can be some agreed with Robert than the 80 truck could it be the best option just looking at it. Those are bigger stator by fact, and the smaller ones are 60 amps ( bigger than any average alt from earlier 70s and all 60s ), some other were 78 amps

BUT being the other one come out from a motorhome, would take both to a shop and test them. The earlier one will fit easier on stock location. The later will fit, but tight