Jerry - the cantleplate is steel, and it is likely original. I have had a
couple dozen Ideale saddles, kept the best of the best, and only the 88, the
alloy rail 90s, and the swallow cut steel rail 90s had the alloy
cantlepiece.
It does crack, sometimes - which can be a big problem. Very unlikely that
somebody replaced and re-riveted the cantlepiece.