I have 64s (actually measure 64" main leaf length) in the rear and 56s in the front. Shackle angle in the front didn't turn out too bad but the springs are damn near flat even though they have 7 leaves in them. They're out of a 77C20 HD I had... 9 leaves in the pack. The shackle is 5.5" long. No, the spring doesn't hit the frame. It inverts first then gets further away (duh). A sharp eye will notice that the cab is moved 3" rearward... the motor is moved 2.5" rearward. I moved the front spring hangers 6.5" forward. The rear springs are out of some late model 2500HD. I pulled one leaf out of the pack (leaf #4). They're still stiff as hell. I'm going to pull the overload out to lose some more lift even though I hate removing overloads. The rear hanger I arbitrarily put where it is based on the shackle keeping the spring from inverting. I figured I'd end up with more droop than I got out of them, that's why I left the pinion pointed down. Since I'll probably end up running lift springs in the front I'll probably drop the rear spring hangers and end up with the pinion pointed up more. I had to grind on the yokes on the driveshaft. I moved the rear spring hangers 2.5" forward. If you see something that isn't kosher, I'm not surprised. A lot of stuff was just thrown together so I could get it on the trailer (including the hockey puck body lift and none of the new plumbing being fastened). It's currently on its 11th day of its build... at day 1 it was a bare frame.