You might write to Ruger with the serial number and ask them. IIRC, the Williams special runs were 5.5 inch barrel stainless, with dual cylinders and I think some sort of gray colored Bisley grips stocks, kinda like the Hunter versions
Could be a Williams' one or an earlier Acusport one. No real difference although later ones had different grip color and the location of the barrel warning changed. Unless one was an absolute purist and needed a specific one, I'd see them both as equal in value, especially as a shooter.
Typically, I see them in the same range as Contender mentioned.