1) The yoke will have to be changed to the heavier duty yoke that fits the 4L80E(not sure of the # of splines). The driveshaft will have to be shortened since the 80E trans is longer than the 60/65E trans. The front drive shaft will have to be lengthened since the transfer case was pushed back by the longer trans.

2)I don't think the transfer case can be used. I would have to think you will need the heavier duty transfer case to mate up to the 4L80E's finer splined shaft.