My trick for bending channel. I used a 1x2 as a spacer. I know all 1x2s are not created equal so you will have to verify against the old channel.
Bend one side just eye balling it. Rotate the channel, put the 1x2 as a spacer, clamp down, remove 1x2, bend the second side. It is not imperitive that the sides are the exactly same height. You will get it pretty close with the practice you will have.
Saves alot of time measureing. Even if you cannot find a 1x2 to match your channel, measure and make one channel, then cut a block for a spacer.
Also, for your curved pieces, bend one side, cut the V notches so that it will bend, then bend the second side of the channel.
I am not sure about your brake, but you should be able to adjust the clamp forward/back the pivot point so that you can adjust the radius of the bend. Too tight of a radius will casue the aluminum to break. Maybe not right away, but over time the fatigue will split it.