Spring under would never fit. There is not enough space for the axle to fit above the springs anyway. If you tried to C-notch the frame, you will contact the oil pan and/or crossmember with the axle. I suppose you could raise the engine........but what is the point?
It could be done with an old "straight axle" with dropped ends if you wanted to keep the leaf spring suspension....but you are back to 2wheel drive again.