When you say Ironwood I assume your referring to Hophornbean or Hornbeam, either is a whiewood and as such just peel the bark and
thats your back. Why do you feel a rawhide backing is necessary? A few pin knots shouldn't jeopardize the back. What style of bow are you looking to make?
Length, draw length and weight, D bow or rigid handle? Lots of variables I wouldn't back it yet until you decide on what the design will be.