You CAN split the cases on a late model OMC Lawn-Boy without removing
the engine from the deck.
First you have to remove all the stuff from the top of the engine. Then you remove the four large bolts (two also hold the engine brake) and two smaller 5/16 bolts that go up from the bottom. The small bolts will stay captured by the bottom of the case.
If you're really lucky, you woln't find 2/3 of the rod cap like I did.
The other third was wadded up between the cylinder and case walls.