Before even looking at the levers, I have a few questions.

1. How did the bike stop with the old levers?

I have similarly aged Dura Ace calipers with the original levers and it really doesn't work well. It's more of a garage queen than rider though, so it's ok. My wife has a similarly aged Ironman with 105 and it stops as well as any modern non disc bike out there. So the question is, did the levers make the performance worse or was it kinda bad to start with.

Before I even considered the lever leverage I would look at routing. How smooth does the cable move inside the housing. Are there any bends or kinks. Does the housing move around inside the cable stops when you pull the lever.

Are the brake pads from 1986?

Are the rims clean?