Are you asking about the "U" bolt to axle, or the spring to frame? The U bolt goes over the spring and into the flange cast into the axle in the front. No seat, just a wedge for caster and a plate for the shock mount. In the rear, the axle is on top of the spring and clamped with the U bolts to the shock mount under the spring. The back side mount is just a U channel with 2 holes that the u bolt goes through. Get a shock mount "lower" and make the other piece if you can not find it in the pile of bits. Here is the picture from the manual for 52 to 54:
http://chevy.oldcarmanualproject.com/shop/1954truck/54ctsm0456.html
If you have the "lever" type shocks then it is different.


Steve H