Bob Ithaca Flues models were more prone, if not notorious, for cracks in the frame thought to be caused primarily by a design flaw due to a lack of sufficient radius at the joint of barrel flats and the standing breech. The sure way to reduce the risk of cracking the frame is using reduced recoil loads. I would select a 1 ounce load producing 1,170 fps or less or a 7/8th ounce load producing 1250 fps or less. Both loads produce a recoil of 15 foot pounds of recoil energy. Remember there is no direct correlation between chamber pressure and recoil.
