In general, the further you pull a bow the more the middle wants to bend. That means if you've got an elliptical tiller a few inches less than your ideal draw length you're almost certainly safe, provided the limbs are bending well and you have no danger areas. You'll just end up with a more circular tiller.
Don't forget that smallest and shortest are two different things - there are SMALLER bows on the ship, but not SHORTER. Yours won't be the lightest by a long way, as some of them were longer and smaller, making them quite a bit less heavy. Also, using American timber will give you slightly inaccurate results and then you have to work out whether the American timber yours is made from is good, average or bad for its species and so on. That's why it's virtually impossible to pigeonhole the MR bows into a weight range. It's also why personally I prefer to always copy one specific bow when I'm making a Mary Rose replica instead of falling into the trap of making "a Mary Rose style bow" because the ever changing results are so interesting. The fact that the same dimensions applied to timber from the same tree can give me 130lb, 140lb and 180lb shows that nicely.
