In theory, BJ8s have the VIN stamped into the right front shock absorber mounting tower, just under the horizontal surface where the shock absorber sits and on the outboard vertical surface. I say "in theory" because many of the numbers stamped there are so imperfectly/lightly stamped that they are illegible with paint on the surface -- in some cases they are not legible even with the paint removed. As far as I know, the earlier models do not have a number there.
Some BJ8s have also been found with the chassis number (i.e., the last 5 numerical digits of the VIN) stamped into the passenger's floor in front of the seat
The gearbox serial number can be used to determine the VIN of a BJ8 that left the factory with that gearbox, but BMIHT will not do a reverse search on a gearbox or rear axle number for any cars. BMIHT will do a reverse search on the body and engine numbers. If the car is a BJ8, I might be able to cross-reference the gearbox number to the VIN and engine serial number. If it's not a BJ8, then I can't help, sorry.