A bit hard to see, but the 4x4 is about 8” long and cut down to about 3.25” tall. That is where the center bolt goes on the skids. Asphir come with a less than robust aluminum space that would never hold much weight. You could jack on that section now with the wood block.
I have a propensity to hit the center of the skid on rocks and mash the center bolt, which also dents the center steel support because all the force is transferred through the 1” spacer ASFIR gives you. The wood block also allows you to jack up the truck on the skid. By cutting the 4x4 down ~1/4” on the table saw it does not impact the rear bolts.