Can your butt handle 300+ miles in one week? That's a serious question and you won't know unless you attempt to replicate it. Try Darth's suggestion. I'm pretty sure he means 75+ on each day too, not total.

Are you going to ride it unsupported, hauling all your own gear? That will further slow you down and add more saddle time.

Other than that, I'm sure you CAN do it.