Larry you understand the problem completely. The ammeter is the bottleneck. And yes, running the extra wire will give the current the alternate path of least resistance and will save the Queen. I do not quite understand excitation either, other than the alternator needs to be positively charged to begin its charging function and some Alts need a second wire for that. (the one that is supposed to go to the battery but everybody just jumpers it over from pin 2 to the main terminal on the Alt).
If you want to actually use that big alternator, then the answer is to remove the original vintage full current flow Amp Meter and go with a Voltmeter. This eliminates the bottleneck.
For those of you who want to continue to use your current Amp Meter, put a 50 amp Fuse in the main line going through the Amp Meter and run another 8-10 gauge wire from the back of the Alternator directly to the Battery. This is from the engineers at PowerMaster, not from me. It looks to be sound advice. I have researched this until my [censored] falls off and this is the very best I have seen so far.
I know that others will say just put a shunt across the meter to do the same thing, but it really doesn't do the same thing. All of your accessories are run off one side of your ammeter. That one wire is busy enough as it is. This protects all of that because the excess current isn't even coming into the cab yet you are getting the full benefit of the higher amp Alternator. I do not profess to know really much of anything, I just research things until I understand them sufficiently to move on to the next conundrum. Email Powermaster and include our conversation. See if they concur. They were very nice in answering all of this for me to share here. I would also recommend doing some additional research on how to properly wire your Amp Eaters. Of course do not wire them in line with your Amp Meter. That has a 50 amp fuse on it!
