Diana,
I once looked at re-powering an S2B with a 3.9/LT85/230, but was advised that the UJ's in the front axles wouldn't last long with constant 4WD. They were really designed only to take power on the occasions when 4WD was engaged, not all the time.
This came from a website in Africa, where they do LOTS of things to Land Rovers as expedition vehicles.
I believe it would be possible to modify the transfer box so that the CDL became a 2WD/4WD selector.
Good luck, it is a nice project. BTW, I think you bought some S2B panels from me when I was in Lancefield, Vic. Hope they reached you okay.
Cheers,
Paul

