Which torsion bars are these?

I'm hoping someone can point me in the right direction. Recently got a 340 powered 1972 Dart with torsion bars identified on the ends a follows: USC 891L and USC 890R. The L was in the left and the R was in the right. Both measure .860 diameter. I'm thinking: These are not stock Mopar torsion bars, right? If not, then is the manufacturer USC? And if so, even though the diameters measure .860 are they rated equivalent to .890 as marked? I'll buy beer for the first right answer! Thanks!!!