That size of an objective is way too big for an XTR FWT. Do yourself a favor and go to something more suitable for the rifle. A more traditional 3-9x40 or 2.5-8x36 will be your huckleberry..
Just for schidts and giggles, here is a fwt with a hubble on top and it isn't even as big as the scope you are looking at putting on your rifle:
Zeiss conquest with 44mm objective (56mm is much bigger):
Same rifle with 3-9x40:
You wouldn't believe what a difference in feel, handling, and balance it made by going to the lighter smaller scope. The bigger scope made it feel very top heavy and awkward when carrying in the field. Just something to keep in mind..
Even better yet is something like the 2.5-8x36:
And just for the sake of XTR featherweights, here's one with a 3-9x40 on top:
A scope like you are talking about would serve you better on top of a tactical rifle, where you are going to have a rail and robust rings to hold the thing. Something more like a CTR:
^^^That's a 56mm objective on this rifle. Just to give you an idea.