Be VERY careful when doing conversions...because if it is not done right and looks like a factory job your resale value will fall through the floor...there is a yacht carpenter in Ft Lauderdale named "Woodchuck" who has been doing conversions for over 25 years...and he's the only guy I'd talk to about this...It ain't gonna be cheap though.
Most 4 cabin boats can't really be converted to owners versions because of the way they are built... I would suggest talking to Kent at Just Catamarans for consultation. Kent is the best in the business when it comes to working on cats. If it can be done he's the guy who can do it... If it can't be done he is one of the honest guys who will tell you...