Thanks a lot for the info. So, it looks like the input of the BBD, MN3002 or TDA1022 is just fixed bias between +/-14v with a 100k limiter. So, I think a 100k trimmer/10k resistor between those two rails would do the trick and then lose some of the fixed resistors in the process to simplify it. The thing that was throwing me off is the MN3002 has a "bias" pin which the TDA1022 does not. But, I think it's just a matter of ignoring that connection on the TDA.
I think I know enough now to work it out. I think I could make a small conversion PCB to fit either BBD on the same board, too. Anyway, I'll strat a separate thread when I have something to show. Don't wanna derail this one with my own nonsense.