Definitely consult a marine architect or designer. Having read two books on the subject already (and seriously contemplating going through Westlawn - money being the current holdup), I know that boat design is NOT an easy thing. It takes considerable planning and thought. Lack of such leads to easy disaster. Bear in mind each boat was designed around specific parameters and considerations (as well as knowledge of boating) - by doing things like adding additional weight up higher you may create a much larger problem than envisioned (btw, there is a calculation to determine how much extra one *could* add without severly affecting stability) in the original design.
The bottom line is, your craft may not be able to handle what you'd like to do so have your plans checked by a competant marine architect.
/s/ Jon C. Munson II