engine convertion

[golfmad]

hi guys just a few questions if any one can answer plz ive got a b3 with a vr6 in it auto but its knockin so engine is out now roughley how much is the auto box worth vr6 it is mint box and still have recipt from vw for it for 2500 .next question im putting my b4 1.9 tdi into my b3 .the b4 is a p reg i no subframe has to go in etc .do i just unplug the engine loom from both cars and fit b4 engine loom into b3 is it that easy .my worry is the diagnostic socket in b4 i will need that to i think .can anyone shed any light or have you done this b4 thanks guys