I too used the decode every entry method. Just to save the effort for anybody who's still toiling, concentrate on
5 Across, 19 Across, 23 Across (Unusual word!), 36 Across, and 5 Down.
A pattern should emerge, along with the coding for BDH & T. These are worked out simply by forming the only words that will fit with the letters you already have and which fit the theme (to emerge as you do it)
According to my calculations, you'll never know FJKQVXZ.