Inside SOUNDS.RFF there's a file called GMTIMBRE.TMB - I guess this is the FM patch bank that Blood uses. I'm not sure what format it's in though, you might have to dig through the source code of one of the Build games to figure it out. Once you know the format it should be relatively straightforward to convert to another format.

I'm not sure what format ADLmidi uses for its banks, but SBTimbre can load .BNK files and read/write .IBK files if you want to create your own OPL instrument banks.

theres a GMTIMBRE.C that comes with both DUKE3D and ROTT source code, would this be what I need?

I'm not a programmer, I only have a limited experience with programming, I don't understand most of what I'm looking at.

Looks like those are hard-coded timbres, but in AL_MIDI.C it looks like there's a function to overwrite those with user-defined timbres. So I guess that's the format they are in? Seems a bit weird though, they don't seem to set half the OPL registers that are available. Maybe there's more somewhere else?

EDIT: Oh no here you go, around this area you can see where those structures are written to the card.

Guess it's just a matter of sitting down and figuring out which byte goes to which register so a converter can be written. I'd do it myself as I want Camoto to be able to do these conversions, but unfortunately I'm a little busy at the moment.