FWIW, Other Historical *is* in Specialty. I don't expect the category to be particularly enormous with this list of styles.
Specialty Beer
31A. Alternative Grain Beer
31B. Alternative Sugar Beer
34A. Clone Beer (non-Belgian)
34B. Mixed-Style Beer
34C. Experimental Beer
27J. Other Historical Beer
P.S. - at ~8% it seems strong enough for Doppelsticke. But it will need to
taste strong as judges don't like to give you the benefit of the doubt on alcohol.
And as a fairly experienced judge, if I even saw this in Mixed-Style or Experimental and someone wrote "doppelsticke: doppelbock-strength altbier" I'd have enough to go on.