I did for a time consider using balsa blocks, but after engaging the little grey cells I came up with a way to plank it and get the desired shape. I did, however, leave the prop lock nut some 4mm clear of the end of the prop tube to get closer to the required gap between blade and hull. As you say with yours, she does sail very well, so much so that I have to reduce max throttle or she is too fast to look right.