Charging system troubleshooting

I want to start by thanking all the members here who have posted in the past answering charging system questions. I downloaded the comments and performed what I think is a comprehensive test and diagnosis of my low charging issue.
The car is my 68 Dart with a Mopar 360 crate motor. Alternator is squareback and the wiring and VR have been updated to post 1971 style. Spark is controlled by a Mopar chrome box. I've owned the car for six years, the motor swap and charging system wiring were all performed by the PO. I've never had any wiring issues and no electrical components have been changed or updated during my ownership.
Recently the ammeter has been showing slight discharge with no load, large discharge with the headlights on. RPM has no effect on charging. It's definitely discharging because the car will start and I can drive it around during the day with no load (other than brake lights) and the car will restart once; the second time it gets sluggish and by the 3rd time the battery doesn't have enough juice to turn the starter.
With batt fully charged, engine off, Bat 12.45V; alternator stud is also 12.45V. Engine running at high idle (2000 rpm) the alternator puts out 12.07V; Batt is 12.2V. Engine running with headlights on the alternator drops to 11.53V; Bat is 12.0V. Is it normal for Bat + to be higher than Alt Bat?
Ran two tests:
With Key On, Eng Off the one FLD wire registered 11.37V. This could be one issue; expecting it to be closer to 12V. Reconnected it to the alternator, removed the other FLD wire and grounded the spade connector to the alternator. With engine running, charging voltage still 12.07V at alt Batt; ammeter still discharging.
Second test, kept the first FLD grounded, disconnected the 11.37V FLD and jumpered over to the Batt +. No change in alternator output.
So it should be the alternator, correct? Removed it and had it bench tested at O'Reillys. I stood next to the guy and watched the test, the alternator passed! Tried it twice.
Can the alternator be functionally OK while diminishing output? Or should I dig deeper into why the FLD wire only registers 11.37?