That is good news, I have both Police Quest and Space Quest collections I can take a look at.
Yes it seems the dual OPL2 implementation is different.
Adlib has one OPL2 at address 0x388/0x389.
Single OPL2 Soundblasters have the OPL2 at address 0x228/0x229, and for Adlib compatibility, also at address 0x388/0x389. Optional CMS chips live at address 0x220/0x221 and 0x222/0x223.
Dual OPL2 Sound Blaster has left OPL2 at 0x220/0x221 and right OPL2 at 0x222/0x223. Writing to 0x228/0x229 or 0x388/0x389 will write to both chips simultaneously, for single OPL2 compatibility with Adlib and older SBs.
OPL3 Sound Blasters have the OPL3 chip at address 0x220/0x221 for bank 0, and 0x222/0x223 for bank 1. Bank 0 is also available at 0x228/0x229 and 0x388/0x389 for OPL2 compatibility, and bank1 is available at 0x38A/0x38B. The OPL3 chip boots in OPL2 compatible mode, so only bank 0 is used and chip outputs audio on left and right channels. Software that detect and use OPL3, will have to enable OPL3 mode through bank 1 when using it, and revert to OPL2 mode when exiting to DOS, so other OPL2 software can use it. If chip is left in OPL3 mode, register data meant for OPL2 will not output any sound, because the output channel select bits are zero and audio is not output to any channel.
Dual OPL2 PAS seems to have left OPL2 at 0x388/0x389 and right OPL2 at 0x38A/0x38B. For Adlib and single OPL2 compatibility, the left OPL2 chip output is configured in the mixer to go to both left and right outputs. To use dual OPl2 on PAS, mixer has to be configured to output left OPL2 on left output only.
OPL3 PAS (PAS16?) seems to have OPL3 bank0 at 0x388/0x389 and bank1 at 0x38A/0x38B, as in OPL3 SBs.
So in theory, it would be possible to convert dual OPL2 data for OPL3 chip for stereo FM. The main problem is that for example with Sierra PAS driver, it is used for handling the whole PAS card (digital sound, FM, mixer..), not just dual OPL2 stereo FM.