Heretic/Hexen FM Patch (GENMIDI) makes doom music to sound very close to beta version.
EDIT:
Patched Chocolate Doom with DMX OPL emulation from press release beta:
Windows binary:
https://drive.google.com/file/d/0B4n8cpbZ9qicd0F1WENtcDBPZzA/view?usp=sharing
GitHub repository:
https://github.com/nukeykt/chocolate-doom-beta-opl
Changelog:
Added Doom Beta DMX emulation.
Replaced DOSBox OPL3 core with Nuked OPL3 core.