Anycubic i3 Mega Top frame extruder and spool mount. This is remixed from Sergiu_I's version to reuse the original Mega S spool holder. I also used the stepper mount included with a BMG clone.

Remove the small horizontal part of the spool holder from the larger arm. Reattach it using the triangular adapter plate using M3 nuts and bolts. The spool holder is then bolted to the top mount using two M3 buts and bolts fed up from the bottom.

Remove the two bolts from the right-top corner of the printer's frame. Now add the new mount and spool holder assembly, reusing the original bolts.

Mount your extruder stepper mount and extruder. I needed a reverse bowden to help the filament feed smoothly.