IABL--
I have also been working on the pitch and roll of various ships, but mainly to prevent the tendency of some ships (tramp steamers, Granville type freighters, LST's, etc.) from sinking in heavy seas. See my brief thread on this topic here:
http://www.subsim.com/radioroom/showthread.php?t=138180 I think I have made some significant progress in this area and I hope to update my STzTrampSteamerFix mod sometime later today.
Privateer is correct, of course, about the function of values such as gc_height and fr_ratio. Lower gc_height to get a more stable ship (less roll). I think you can also get more stable behavior by altering the mass and surfaced_displacement values as you indicated you have already tried. Usually, lowering mass results in the ship sitting higher in the water--try the opposite in order to get it to sit lower (you may also have to increase surfaced_displacement to help achieve the effect of a heavier ship). I have also had some success altering pitch with fr_ratio, which seems to be set to a default of .5 for all ships.
I have not tried altering LR or UD drag yet, as I did not know what those values did! Thanks, Privateer, for shedding light on that!
I will investigate what effect those values have on the changes I have already made on my ships later today.