The '79 model year bike, has a pressure switch to operate the brake light, so it is different from an '81 year bike, the US bikes for that year, came with dual front discs, so it won't fit your brake configuration .
I've gotten three sets of brake lines from Speigler, they will help you to get this sorted out, great people to do business with .
Send them an email with what you have and see if they have that configuration in their data base .
Worse case scenario, you can send them your brake lines and they will make up a set for you .
Usually quick turn around times, less than 2 weeks .