I used a small file to key the surface so it should adhere well enough. I need to remove the paint from this arm before testing it as my other one is silver. I just can't ride a bike with odd cranks.
The areas that were worst affected were the top and bottom of the pedal stroke - 9 o'clock and 3 o'clock weren't so bad.
A better picture would show the transition from the aluminium interface at the front of the arm to the area filled with JB Weld at the rear...
I covered all of the tapered interface with JB Weld but tightening the arm pushed out any excess material which left it only where it was needed.