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The squeal will probably go away from just driving the car 50 or 100 miles country, or an afternoon of city driving.

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Time to put vacuum and hydraulics on the back burner and deal with the friction.

The squeal is caused by the brake shoe vibrating when pressed against the drum, usually due to the surfaces not mating smoothly.
In the pictures, the shoes look to have plenty of material and don’t look glazed, and the drums don’t look bad but you said there are some ridges. You should be able to bed the shoes to address the issue.

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What's the best way to bed the shoes? Pull the shoes, put sandpaper between them and the drum, and lightly sand them down?

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The shoes and drums seem to be in reasonable shape based on your pictures, description, and how well the brakes are currently working so it doesn't seem that you need to work on the individual surfaces. Unless the ridges you said you have on at least one of the drums are wider and deeper than they look in the pictures. You should also check the drum inner diameter and the size of the lip on the inside edge. If there are no issues requiring other preparation, proceed with bedding the shoes and drums so that the two surfaces are worn such that they mate smoothly and have the maximum contact area. This has to be done by wearing the shoe and drum together.

There are many similar bedding procedures, but they all go something like this:
- Find a long reasonably straight road that you can go about 60mph on and has very light traffic.
- Do 5 or 6 60-15mph reasonably hard, but not panic decelerations in succession. You want to cause wear and generate heat.
- Drive a while to cool the brakes.
- Do another set of 60-15 decelerations.
- Cool the brakes.