Here is a very good reference for the Duplex Drive Shermans, sorry DJ I know it's not the M-3 with wading trunks.
http://www.kithobbyist.com/AFVInteriors/dd/dd2.html

Rob--It would be quite a feat to see someone put together a DD Sherman. Gunnie can probably do it in his sleep. The rest of us can only hope Tamiya gets the urge to be really inventive.
DJ

You flatter me Sir - but I'd be hankering to give it a go alright! A Tamiya DD M4 would be awesome. I don't think anything that company would undertake could be anything less.

Gunnie

Rob/Gunnie--I can only envision what a nightmare it would be to construct a DD Sherman. For example, you would have to extend the water wings in order to demonstrate the flotation device. So the ribs and fabric would present an engineering challenge. Once you did that I believe the top side of the vehicle would be a basic 75mm Sherman. In the rear of the engine access, you would have to place an accurate propellor unit. Boy, the water wings would be tough. I can envision having one or more in a diorama with that VLS half submerged (and easily duplicated) Sherman now on the market. If memory serves me correctly, the British launched them on Gold, Juno, and Sword beaches for the Normandy Invasion. They did not do too badly. Whereas the tank battalion supporting Omaha Beach floundered. They were launched too far from the beach into too large a swell. Tragic. Well worth thinking about replicating. Hell, I can hardly get the time to build them out of the box. But, oh to dream!
DJ :-)