Marshall (http://www.mm4x4.com.au/)has only recently developed a kit for MN 4 speed auto's. Have had a Lockup Mate installed in my MN for 2 weeks and have done some k's but not towed yet.
The 4 speed in these is pretty hopeless in drive mode as the TC spends most of its time unlocked, resulting in mushy feel,high AT temp's and increased fuel usage which is even worse when towing. Up until now to overcome this I have spent most of my time driving in sport mode which is better but still not great.
This kit has totally transformed my auto. In sports mode its basically a clutchless manual in 2nd 3rd and 4th and in drive mode it locks solid at anything over about 70 kmh.
I won't write up on what it does or how it works as all this info is available on mm4x4's website.
I have no affiliation with mm4x4 but believe a good product and backup deserves a thumbs up.