Unless you are a purist, since the horse has left the barn on your choice of alternator, one option would be to drop the ammeter altogether, peace of mind is worth something and go the voltmeter route. In the interim, get your voltmeter and do the swapout with the original cluster as a winter project. I've never been good with electricity, but it helps me to think about it like a fluid, water for example. Amps = volume or flow of electrons, volts = pressure, resistance = restriction, relay is a valve, shunt = bypass, etc. So you have this big ole pump (alternator), putting out maybe 3 or 4 times the "volume" or amps your system was designed for, and you need to restrict/bypass the flow down to where your gauge can read it. Seems like too much work to me, instead let's just measure "pressure" go with a voltmeter, and move on.
