C404 pilot experiences a loss of power after takeoff at maximum weight from a high altitude airport. The aircraft will not maintain altitude; but the propeller is not feathered until the Tower is informed of the return; which takes three attempts.

Narrative

I was close to MTOW. I was given a heading of 140 and told to climb to 9;000 FT. Engine number 2 began to run very rough and lost power. I tried to adjust the mixture and turned the emergency pumps to high. It had no effect on the engine. I lowered the nose to maintain airspeed and started a turn back. I declared an emergency and told the Tower I was going to return and land on Runway XXL. No answer. I continued my descent and turn back to the field. I was able to maintain airspeed; but only in a descent. I called Tower again and told them my intentions. They responded with 'what about XXL?' I told them for the third time what my intentions were. They cleared the runway. I then was able to feather the prop; pull the mixture to cut-off; and lower the gear. The landing on XXL was without incident. Inspection showed the accessory case had failed and basically blown off the back of the engine.Lessons Learned: 1: Have your immediate actions to a point where they are instinctual. At this phase of flight; you have only a few seconds to get those actions done and maintain airspeed. 2: Have a plan before takeoff. Know where you are going to go if you lose power. 3: If an engine is acting up; best get it feathered rather than try to decide if it's producing power or not. Most likely; the drag from the unfeathered prop is more detrimental than any power you may be getting from a sick engine; preparation; preparation; preparation.