Getting the trailing edges cut and trimmed to butt together perfectly took a little bit of time using hand tools, but pretty happy with the result.
Much of the flap assembly required to cleco the entire assembly together to final drill, then disassemble for cleanup. I ended up 3D printing a spacer for the hinge brackets to avoid putting in appropriate washers during assembly.
I used the squeezer to double-flush rivet the hinge brackets. They didn't come out quite as pretty as I was hoping, but look pretty flush in the end.
For the final riveting of the trailing edge, the instructions didn't provide much information on. I ended up back riveting all the trailing edge rivets, which worked quite well. The only trick was to initially drive the rivets along the axis of the rivet, then finally setting them parallel to the trailing edge.
The final flap turned out pretty square along both the hinge and the trailing edge.