I don't know if the other members have encountered this, or may be I don't have the best tools, but I have separated both, st185 and st205 transmissions from their respective motors, and there is this pesky bolt that none of my ratchet wrenches or breaker bars cleared. On the st185, I stripped the bolt, so I had to chisel it out. On the st205 I learned from my mistakes, and used a 6 point spanner + piece of pipe.
As for the removal, abeans pretty much sums it up. I grabbed one of those movers blanket from harbor freight and careful placed engine on its side (crank pulley facing the ground), and used a hoist to slowly lift the tranny. As you lift the tranny, you twist and pull until it separates.
Alternately, I have also removed the tranny by lifting the engine with a hoist and placing it on a pallet and give it just enough height for a pull and twist motion on the tranny side.
Had no issues doing by my self, although a pair of hands always comes handy.