For one you have random connections to the engine that you must connect, (Wires, fuel, exhaust, intake, cooling system, air conditioning, etc) Then you have to mate the engine with the tranny. after its mated with the tranny you have to put the engine onto its mounts and start wiring everything back up. its a rather large job compared with the simple unbolting of eighteen same sized bolts lowing the transmission and then putting it back up and putting the bolts back into its place. And if the engine is being rebuilt while its out, it would complicate things also.

__________________
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.