Dave, for what it's worth, we've been talking about similar on this
post.. (Not the alternator part, but the ammeter part) .I recommend abandon your ammeter, leave it there for looks or replace with voltmeter if it will look right in ammeter hole. If not, elsewhere.
I would not modify the dimmer until you call them. If the kit is for a 47-55. It does not say in the literature that you have to modify the switch. Find out what the deal is. I don't know if "does not fit" means mounting holes off or an electrical issue. Both the 47-55 and 55.2-59 and up, have mounting ears with threaded holes. Doesn't it just come in from motor side and screws go in from cab side?
Idiot light= no resistor needed. Without idiot light supposedly you can hook it up with a resistor and diode or just a resistor wire. Your schematic diagram supplied with the AAW kit should give you clues as to what they designed it for regarding resistor, etc. Read it carefully and all the notes. I realize you said it's designed for SI. 47-53 did not have idiot lights, so I would think AAW has that covered or will advise.
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The conversion harness from SI to CS is one wire with a CS connector on one end and SI connector on the other. So I would say that as far as resistor/idiot light/etc. requirement.......... it's the same.
I'm guessing that: if the kit is for SI, and CS is electrically the same on most issues, and the kit is for Voltmeter, and you abandon ammeter, you are good to go.
The SI (System Integrated) and the CS (Charging System) have armature/winding/regulating/bearing differences. CS being the more modern. I believe the external wiring is the same.
I second the comments by JimSears.