Hi, so i have a 1970 d100 and am trying to replace the front shackles. I ordered a kit from this website: http://www.eatonsprings.com/shacklekits.html.
When i slide the shackle through the bushing on the frame, there is about 1/2" play in the shackle. I was wondering if i would be able to safely add a few washers to one side of the shackle, or would this mis align the leaf spring?

 

Without pictures, it's hard to visualize, but the key word is "slop" and "play."

The answer based on that is NO

The shackles have to be stiff enough to prevent side-to side movement of the axle as the vehicle body moves, in corners, on road crowns, etc.

On the older "rigs" which had a drag link from the steering box that went crosswise of the vehicle, this condition easily caused steering problems, because as the axle / body moved, the vehicle "steers."

In fact, on my old FJ-40 Landcruiser, which variously had a 360/340/318 for power, I replaced the inboard strap of the shackle with a piece of angle iron, and interconnected the two shackles with a leaf spring. I believe the late IH shouts (Corn National Interbinder) did this, and it REALLY tightens up the front end and handling.

The point is, shackles make a HUGE difference in handling.