Did you swap coil connections? Wrong polarity and spark is much weaker.
Thanks for the tip. I've swapped the ignition coil wires now.
And thank you guys for explaining the distributor points as well. Makes sense.
I've rolled it again, this time in top gear (not 1st gear!); the points open and close fully. The coil is showing 12-13v on both connections with the points open, and it gives the same reading closed: about 12.9v on both sides. Also, I'm only measuring 0.2-0.3 ohms resistance (not kOhm, just single-digit Ohms). Bad ignition coil?
That coil is a bit low, did you take both leads off before measuring?
looks like you have an issue with the distributor. Can you measure resistance between that beat up flathead screw in the distributor and chassis and between battery negative with the keys removed from the ignition.
You want there to be low resistance as the points closing shorts the coil to ground allowing current to flow. Also check resistance across the points when closed with the wire disconnected from the coil that comes from the distributor