Now, that was not that easy, after all. If one is free to fit a new mast in any position, it is no problem. However, if one is to make use of the original mast, going through the original partners, then one must struggle. The problem is a combination of short mast and its position. That forces one to draw a low AR sail to push the CE as far aft as possible and to get a decent sail area. I ended up with the shown sketch, below. I actually used one of my 7-panel master plans, the one with AR=1.95. By cutting off the lowest panel, the AR was reduced to 1.72. Then, by scaling this 6-panel sail up until batten lengt, B=5.50m, I ended up with a sail wit SA=39.2sqm, versus 37sqm on the lug sail. The CE still appears to have moved a bit forward. Maybe it would make sense to cut the sail with the max camber point at 42% from the luff instead of the usual 35%, and then try it with the original mizzen. One may still need to add a foot or two to the foot of the mizzen - or not...
See for yourself.