Measure the distance from yoke to yoke to determine the proper length driveshaft.
Here is how.
A Dana 44 rear pinion is slightly longer than a Dana 35. If you have any suspension lift it likely offsets the difference and should be fine. See above though and measure.
If you have more than 2.5-3" of suspension lift you should buy a Double Cardan rear driveshaft to avoid vibes (it will also require rear upper and lower control arms to adjust the pinion angle).
Also, before you go changing driveshafts, what else do you plan to do to your Jeep? If you're planning to lift it more or do a tummy tuck you will just be buying driveshafts again or having them altered.
I don't know why you would need to swap the front driveshaft unless something at the yoke's and ujoints don't fit.