Installing Echo Speedfeed 400 head on Stihl FS40C Curved shaft trimmer

The Echo Speedfeed 400 doesn't fit the Stihl FS40C straight out of the box, but I was able to install it by re-using a few parts from the original Stihl bump cutter head, and drilling out the silver Echo bushing with a 3/8" drill bit to repurpose it as a spacer bushing over the shaft.