Sorry - my mistake - too idle to go look at the plans out in the garage.
Front end - look at romeolima.com, fuselage section. There a few photos of how to deal with the front end, with an extra gusset.
The length of angle is definitely riveted to the fuselage skin for its entire length.
At the aft end I think your idea of a bracket sounds good. Look at drawing 27, section E-E'; there is a convenient bolt at the lateral margin where the angle runs to, though if the rear of F413 and the rear of this piece of angle are at the same level at F403, the bolt hole is a little high. I think the limiting factor is the front of F428 as this will determine a minimum angle for this bit of angle. (We need a name or number for it!).
Unless anyone chimes in with better info I think this is what I'll be doing.
Chris