1969 280SL engine re-assemble

[Tishs Auto]

Hello, I recently had a customer bring a very nice 1969 280SL into my shop in a box. Engine was completely disassembled. I have new main bearings and they all have a oil hole and groove except one. I am having a hard time finding someone who can tell me where the bearing with oil hole only goes. Front or back?

Any help on this would be helpfull

[drmb]

That one belongs to # 4 main bearing.