Got it! It took a few days of penetrating oil. Then I removed the cap and rotor. Since there's no room there to get a good side grip on it, I put one large channel lock straight down on the distributor and another channel lock gripping the first one. Gave some gentle pressure but forceful pressure and it moved.
When I first checked the timing it was somewhere around 16° BTDC. After I moved it it was 10°. And I can feel it when I drive. Feels like a new car.
At some point I should try to work it out of the block, clean it up, and replace the o-ring. But that's for another day.
