Annoyingly the hole at the bottom is narrower than the top so it won't be a perfect fit.
You could make and use one of these: https://youtu.be/VkY879pMafE
and soak it in wd40 for a few days before you're tryig to hammer it out.
Good idea, I'll investigate.
Side note, I'm doing all this in a small flat with no shed/garden/etc. which makes power tools, vices, etc. and the like impractical.
@frankenbike started
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You could make and use one of these: https://youtu.be/VkY879pMafE
and soak it in wd40 for a few days before you're tryig to hammer it out.