RESOLVED. The spark I saw made me investigate any wire sources that could produce it. I found the problem the moment I begin inspecting the passenger side Alternator. One of the heavy Red wires to the ALT had been hard-pressed against the capacitor- shown in picture with carbon arc/pit. I taped the wire, but I'll rewrap it with something more substantial later today.
I found a 30AMP headlight fuse blown in the fuse box. I don't know that the short would strain the headlight circuit, but the fuse was not actuall burned out so much as melted. Anyway, after taping the open short, I started everything right up and drove for an hour without any problems.
There is the matter of the fuse block though. The phenol/plastic holding the blade connector is allowing the blade of the fuse to barely be pinched in place. I'm going to disconnect the batteries and see if I can tweak the connector to grip the fuse more tightly. I don't want to lose headlights on a night trip.
Any ideas on an alternate work around?
P.S. Thanks to all for their input. It helps make me a better mechanic whenever I have to really look at systems I don't generally work on. The most I have done with the GP system is replace the controller card and the plugs. I got a bit of an education this time around.