Thanks for your suggestions!

The pinch bolt and clamp are loose. This engine also has a small scale adjuster with a cam bolt, which I read is for a quick manual adjustment to compensate for poor fuel. The retaining bolt is also loose. This device is free. They both move independently of the distributor housing.

I've tried several things up to and including using a slide hammer with a gear puller attachment. No luck.

I may try cooling the steel distributor housing next...

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights