Caliber restriction rules are often written this way. They make little sense. I agree that the 10mm should be legal. The .22 Creedmoor should also be legal for elk, but it's not, and the .25-20 Winchester is. Go figure.
If you did use your 10mm, I doubt you'd get ticketed. If you got ticketed, you could make the argument in court and the judge or jury might toss it. After all, you're using a more powerful cartridge in every metric. Who would argue against that?
Another option would be to load a long bullet like this and single load it. That would get you past the 1.5" requirement.
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