Might not be a lot of metal left after that rust is removed.
Many people are against restoration for their own reasons; but in the end you should do what you want to do. It is your business. That said, not sure that this is a good candidate for restoration. But, if you decide to work on it I suggest that you immerse it in straight, undiluted vinegar, which is lightly acidic and works wonders with rust. It will remove decals, tho', but I suspect this in not an issue here.
Put it in a bucket, get a big jug of vinegar and totally cover it. After a couple of days take it out and use a bristle brush on it to remove loose portions; then re-immerse. In four or five days it should be back to the original steel, but it may take longer. When it has reached a condition with which you are happy, dry it and spray thoroughly with a rust preventative such as Rustoleum. This final step is essential because it will start rerusting immediately. Then, you can display it or restore it. Good luck!
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Personally i would leave it alone, from these photos it would appear that the metal is already very thin and the large buildup of rust bubbles can only mean that removing them will cause a great deal of damage, it could leave you with very little helmet left, any restoration after that will leave you with 80% filler and almost no history.