Here's the 12hp engine dropped in and coupled to the driveshaft.
The hardest part of this job was getting the 12hp to slide in - because of the longer crank throw, the 12hp Kohler has a dished-out oil pan (my old 12hp Kohler is pretty much the same engine but with a shorter stroke and a flat pan.) - while, at the same time, getting the end of the drive shaft to slip into the bushing in the center of the clutch driver disk and getting the clutch friction disk to engage the dowels. My better half was called into play to get things lined up while I muscled the engine around.
The next thing was go get the engine line up on its mounts to get the bolts started. I found that I had to loosen the engine mounting channels on their new solid mounts so I could slip things around to get everything lined up, then finally tighten everything back up.