There were still plenty of alloy butt plates around in the 80's and 90's when they were withdrawn. The trouble with the alloy ones was that they were not cast but sintered (? might not be strictly correct I fear but close.....) so they'd fracture and snap VERY easily. Whereas the cast and machined brass were a lot more forgiving. The true answer re longevity is that if they weren't broke, we didn't replace them. I don't think that there's a reason to bend a butt plate to fit. You rasp-to-shape the butt to fit the butt plate