Snazza, its been thought about but its not just the engine, its the ancillaries too.
The 3200 is wet sump, ie it holds its oil in the sump pan, where as the 4200 is dry sump, ie it has a separate storage tank for the oil, a bit like the coolant header/expansion tank. This is done to make the engine shorter so it will fit. The bonnet on the 4200 is very different, its humped to allow for the engine so I recon coupled with all the ancillaries, it just is not going to fit in the 4200 with out a lot of cutting.
If you were doing it, you would have to change the subframe, wiring (nightmare) and the bonnet.
The best way to do it would be to take the 4200 engine out on its subframe and drop the whole unit in
Then there is the small subject of the transmission/transaxle, only for the brave I feel.