Welp, that's the question that I would like to know also. I don't know of anyone that has tried this yet. Many peeps wanting to ditch their A43Dx for a W58 5-speed, but swapping Auto A43DE's for a A340E (even temporarily)..... Wish I had a better answer. I "think" the size dimension (lengthwise) is different, but don't quote me on this.
You can swap them and it will work, but the MkIII transmission is semi-electronic so the overdrive won't function. You could probably find some way to install the MkIII ECT at the same time, but I don't know anyone who's tried this.
hey i got an 85 automatic will it work with out the electronics pluged in?????? :?: i have a bad w58 that still hasn't been repaired. can i just hook up the oil lines to a cooler and have all gears except overdrive????? :?: i've really been thinking about putting it in BUT don't want to if it's not going to work. please let me know cuz it's pretty much do or die right now with this car. if it works i will keep it if it don't it might just go to the junkyard or to some body thats needing a great car that has a w58 laying around. and yes the automatic is longer you will need to have the drive shaft 2. different trans crossmember aswell. just fyi