Start by removing the pommel using a spatula or prying tool then remove the screw from the battery cover.

The two halves are held together with six screws so it's easy to take apart.

Carefully disconnect the speaker and slide switch connectors from the main board.

Desolder wires for the pogo connector, push button and the vibration motor.

You can splice wires to extend the cable from the pogo pin connector. 

Attach a 2-pin JST cable to the battery holders terminals so it can plug into the Feather.

The push button wires can just screw into the Prop Maker's screw block terminals.

You'll need to cut the trace on the back of the Feather to disable lipo charging so we can use Alkaline Batteries.

Add another JST cable for the slide switch and insulate the exposed pins on the back of the Feather with some Kapton tape to avoid shorting.

Then we can plug everything together and close it back together.

The Feather fits between the old PCB standoffs with cables tucked underneath the board.