Since it has not yet been said, I will take this opportunity "Steel is Real"
As far as a 1981 Fuji, another I saw was a handmade lugged steel triple-butted Valite frame.
bianchigirl maybe able to help as another of his prior posts noted:

Here is some info on Valite. Apparently it is between HiTen, Mangaloy and ChrMoly. Fuji made tones of bikes with it in various buttings https://classicfuji.com/1982_04_Information3_Page.htm