I'm considering using "Elysees" handlebars on my recently acquired 1986 Nishiki Continental.
Here are the bars (I already have them from a previous project):
Compass Bicycles: Handlebars

And here's the bike:
https://www.bikeforums.net/classic-vi...l#post16808902

Roughly how much longer should my stem be to accommodate this change?

As long as you need it to be? Nobody is going to be able to tell you what fits you better than you can.

I agree that's difficult to say. Do you mean longer extension or longer quill? Are you going for a more upright position? Where do you tend to place your hands on the drop bars, and where will you put them on the Compass bars?

I'd start with the current stem and figure it out from there, or play with an adjustable stem if you have one.

I meant a longer quill. I tend to ride just back of the brake levers. I'm thinking of a more upright position, with my hands "round the bend", i.e., on the section of the bars roughly parallel to the bike.