As far as the spring leaves go, I'm not sure what is required. It would depend on the length of the U-bolts supplied. What I will add is that I see no need for the overload on a performance type suspension. The back of the spring needs to "work" so if you have the HD spring pack...I would definitely take a couple out. I have the 3 leaves on mine & works well. You need the suspension soft enough so the shocks control the movement, with too much spring...they are (for the most part) going for a ride.
Caltrac makes two set-ups for our trucks: Stock (for the axle UNDER the spring) & Flip (axle ON TOP of the spring).
Get with Chris (Capt.) he is a vendor for Caltrac. Lorne