Astonishingly, the size I chose for the fan shroud pretty much exactly fits your average spring coil starter for a lawnmower. It's amazing.

The cringeworthy point of no return.

Hard to really see here, but we'll send the router through one more pass making the hole slightly deeper and wider and the spring coil and pulley should fit perfectly.

It isn't gonna go RRRRRRNNNNGGGGHHH when she pulls it, but it will spin up the fan blades and the pulley will return the cord automatically. Excitement!!!