Well the weather cleared up on Friday just in time for it to get dark so I didn't get to things until Sunday. Since I don't have an induction ammeter, I decided to pull both the battery and the alternator and take them to a local parts place that does free testing. This had the advantage of getting the battery fully charged for free (it was down quite a bit) and I didn't have to play around with test leads in tight quarters (getting them in with the engine off was certainly my plan, I just didn't think they'd stay).
Turns out that both battery and alternator tested out A++ so the problem appears to be the voltage regulator. I'll be placing an order for one shortly and will get that installed after the New Year.
Thanks again for everyone's input and Happy Holiday's to all.
'87 560SEL 267K (177K on motor) Blue/Blue
'98 Buick LeSebre 60K (wife's car)
'56 Imperial Sedan 124K
'67 Dodge Monaco 130K (Sold)
'87 Chrysler 5th Ave 245K and going strong (sold)
'73 Plymouth Satillite 175K (sold)
'96 Chrysler LHS 80K (totaled)