[C320-list] one bad cylinder

[Jane & Ken]

All,  I have a 1995 with the perkins (Detroit) diesel, three cylinder M-30.  One cylinder has no compression--number three--The other two cylinders work fine and will rev to 4000 rpm in neutral.  In gear only rev to 2000 rpm and reach only 3/4 hull speed.
  The question is,  has anyone pulled the head while the engine is still in the boat?  Seems as though there is sufficient room to do that however the marine "worker bee" say that they won't attempt it.  Any advice is welcome.  The engine is 'new' with only an original 262 hours.  THANKS,  Ken  #219  OBUOY