Here is what I did on the rear:

I found a pair of leaf spring perches on an old rearend I had. I unbolted the axle and dropped it to the floor. I removed the shocks and dropped the driveshaft to make it easier to move the axle around. You may not have to do either. Then, I clamped the leaf springs together with a C-clamp before I removed the leaf centering pin to flip it over. You will have to remove each leaf spring from their hangers and put them under the axle. Sit the spring perches on top of each leaf spring and sit the axle on top of the spring perches. The new spring perches should be on the exact opposite side of the axle from the original spring perches to keep pinion angle. Clamp everything down using your original lower shock mount plates. Weld the rear axle to the spring perches.