The bolts are labled as "a" in the FSM headbolt tightening diagram. And others have said there are two in the engine and two on the outside.

Question- Are these bolts labled "a" long enough that dropping down into the engine uppon removal is not a risk? I would imagine they must at least be as long as the head is tall, right? Just asking because I am about to pull the head on my 240D