A mechanic would heat up the nut a little and take it off in 5 minutes. The sears flair wrenches are not good enough to remove the nut, the metal is too soft. Been there done that.

You could pay a mechanic $20 to loosen the nuts and finish the job at home. Once the nut is unscrewed, the original flair needs to be cut off, the nut replaced, and the line re-flared. There is plenty of brake line to do this.

The problem with a flat vice grip is that it only grabs on 2 of the six sides, you could wind up bending the brass nut out of shape. Almost better off with a pair of chanel locks.

Klaus
--
Proud owner of a 1967 220S. If I had more room, I would have more Volvos.