Basically, I'm interested in having S&S coupler installed in an old (steel) frame (mid 80's Bianchi). Any ideas on who to go to and how much it will cost would be a great help. I am in the Washington DC area, and have no issues waiting 3-6 months... or more. The intended bike will be a single speed /fix gearfor long all day hauls.

https://www.sandsmachine.com/fbplist.htm

Bilenky in Philly advertises that they do retrofits. Cost is 395, plus more for re-painting. This is in the card for me one of these days . . .

Yup, all good advice above.
However, there may not be any S&S fittings available to fit your older tubing.