I made a jig so I could work on the rollbar while the car is away from the workshop. Makes a tricky job a little easier, notching tubes can be tough on the brain! Especially if the joins are to be TIG welded, as then it's even more critical that the tubes fit tightly.
Once I had one of the backstays fitting right, I traced the scallops with paper and transferred the cut line onto the other backstay tube. Worked great, saved a lot of fiddly work. I've never done this stuff before so am pretty slow.
Once I had the backstays finished I mocked up the diagonal member in alloy. I made a rail on the jig that the tube could sit on so I could figure out the scalloping easier.