Without a DBX unit, you have to reintroduce two things. A tone adjustment to cope with the EQ shift pre-emphasis introduced on record. It probably sounds a bit bright that needs taming and the dynamic range is squashed, so you need something to expand it rather than compress. With fiddling, you will get a result that works. It just wont be exactly what it should be, but musical taste back when it was mixed would probably need a remaster nowadays anyway? If you want it to be ‘correct’ you’ll have to seek out a proper DBX emulator. I’m not sure the word we used, ‘decoding’ was ever correct really, it was never really coded was it? Just companding and boost on record removed on replay.