Did you move the axle backwards 1" when you did the flip?
Notice the hole to the left of center in both the home-made (top), and the mopar perch (bottom, with a re-drilled hole to the left of center).
This moves the axle back 1" to account for the angle of the leaf pack when you do the flip, so you shouldn't end up with a short driveshaft.
Oh, wait. You said it's too short now. That's odd...