Transmission shifting
 

I decided to convert my 83 turbo diesel to manual transmission. In my search for a 240D 4 speed manual tanny I ended up with two. One from an 83 240D and another from what I think is a 78 or 79. The 83 is a one piece unit and bolts up to the engine with no problems. The older unit is a two piece box and has a different bolt pattern. Can anyone tell me what the older unit is and why it has a different pattern? It was my understanding any year of 240D would be compatible.