Ive only built one kayak - and it still isnt done yet, BUT, before I'd doctor up an established design, Id go the distance and learn to handle it properly. After that, make a judgement. I get the feeling that your seat is too high like by an 1 1/2" however. If it isnt a seat problem, Id give some thought to appreciating the tippy characteristics for whatever reason it was designed like that. Very often, swift efficient kayaks are a bit tippy due to either hull shape or narrow beam. Theres hard set reasons for this. Personlly I'd take on the learning curve to balance a hot performer than the rock solid stability of a barge. Do you want to push water out of the way or slice thru it?

Pete
experienced barge paddler waiting on the completion of his tippy multichine - happily.