I would like this information also.If you cannot find a freezeplug tool, you could always have a good machinist make one for you. I'm sure it would be borderline expensive, but it would be the right tool for the job. Also, it would be a lot less expensive than a new engine.
Some one long ago published a design drawing. I just tried to upload it, but apparently the image is too large, at 1.72 Mb. I'd be happy to sent it to you as an email attachment.