Ive got a 1977 DV20 that came with my Pearson 36. It wasnt installed and still isnt. From what the last owners said, the motor was great and never gave any problems, but the gearbox gave out. If i would find another gearbox, i would put the motor back in my boat. Its got a ZF gearbox. Ive got all the parts to it somewhere.
You might try here for gear box parts.