If you're staying SUA, the ubolts will need to be pretty snug once the spring perches are installed on the axle. Then it doesn't matter if the tires are on or if the axle is sitting on jackstands, either way the weight will be on the springs. I would tack the perches before pulling the axle back out.
Once the ubolts are snug enough to hold the axle to the springs, it will require a large pipe wrench to rotate the axletubes, or a floorjack under the pinion.