I would definitely be interested in a 4x4 conversion. I do not think the use of the deck is going to be an option though. Unless you could find a really small top loader axle, the drive shaft will be in the way. I do know the front axle on my dads x585 JD is a top loader. I have never really looked to see if it could shortened. It is definitely to wide as it sits for a cub.
And remember the trans case will have to driven from the output shaft of tranny. Or else you will only be able to use 4x4 in one gear. Have you looked at a primary drive chain from a Harley ? I am pretty sure that a cub would not break one of those. Same idea as a timing chain, just better.