Hi Rich,
The Levy Racing shocks are (or at least they were when I bought them) always the same length front and rear, pin drive or regular IRS. Due to the different geometry of the pin drive suspension parts, this will not allow sufficient travel at the shock when the ride height is correct. With pin drive you should therefore either use longer shock than regular IRS, or relocate the upper mount.
I am trying to figure out which way to go now....
Lukas