Alt was spinning, just not enough.  I could clearly see the pulley turning.
Dad suggested I try spinning the alt w/ a drill or air gun and see if I get a reading (while the key was on of course).  When I did that, while holding the probe to the alternator output, the voltage jumped about .15v volts from the key on, engine off reading.
I tried again w/ engine running and got about .05v over my baseline, so I knew it was being turned, but figured it had to be my belt, since James had mentioned charging issues and my belt wasn't exactly what you would find if you googled for SBF 5.0 serpentine layout. Then I figured that it must be my belt.
Once I added the new pulley and moved the tensioner to a more traditional layout, it was much harder to get the belt on and the belt was clearly tighter, so I figured that was good news.  Once I started that time, I got a 1.2 or 1.3v more than my baseline and was good to go then.

Time to button things up so I can get this car on the road.  Been too long spent on this swap