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baileyscream
MKB_RO.inf is on the root of the disc and is visible in Windows (may have to show hidden files) and is not encrypted so you can open with a hex editor.
If you look at your current 3.55 DRL files (2 of them located in dev_flash3\Data Revoke\DRL) in a hex editor, you should be able to copy and paste from the disc to create a matching DRL (check the wiki for more info)
If not, you can use DRLTools that was released some time ago (after the first downgrade broke bluray) which will create a valid DRL file from the MKB_RO.inf file for you automatically (Windows based tool) whcih you can just copy over.