Hi Phil,
Here are some of the specs on 731OS race tube set.
Introduced in 1992, double butted tube main frame with 8
raised ribs on the butt, as opposed to 708 which had no butting only 8
raised ribs,
it was a variable strength technology; head tube and fork was 531
steel(700/850 n/mm2), main tubes (750/920 n/mm2),
the stays were 753 or 725 steel the spec sheet dosen't specify(
1080/1280n/mm2).
731OS was a nice tube set I built about 10 frames with it in the 90s
had only good response about it from the purchasers.
Hope I helped.
God bless,
Anthony Mezzatesta
Mezzatesta Custom Cycles
909 Berkley Manor Dr.
Cranberry Twp, Pa 16066
724 498 4191