I was able to finagle the double offset rivet set around/through the angles as necessary to obtain access. I used a Taylor 2x rivet gun for my entire build. A 3x gun might also fit, depending on the length of the double offset rivet set.
Here's a pic of that process when I riveted those together
. You can see the gun laying below the idler pulley.
Requires a different hold on the rivet gun, however it's quite controllable.