There may be other solutions

Given this problem, I'd frame in a an appropriately sized trough, lay out the
mud pan and hoe, hop in the ol' pickup and get a bunch of WhoopeeCrete and a
case of vintage brew and call my buddies to spend a happy Saturday, mixing,
pouring and smoothing. With the pour complete, shove the anchor bolts in their
proper location and after curing start your wall. You already know about
square, plumb and level, right? And adding the magic bonding agents to the
concrete, and cleaning the old slab first? HTH

Joe