Summary

The gears have a bigger module, meaning the teeth are bigger. They are also herring-bone gears, but still noisy.

The 19 tooth gear combines with the 8 teeth shaft, The 21 tooth gear fits the output shaft (original is OK, no need to print a new one).

The reduction ratio is not kept, but it does not deviate a lot from the original.

Your housing may need sanding to enlarge the hole for the 8 tooth motor gear.

For customisation I used Janssen86 customizer. You can find it here:
https://www.thingiverse.com/thing:1587923

Thanks Janssen.

EDIT: if you plan to use the metal shaft version (https://www.thingiverse.com/thing:3398973), you need to sand the bottom housing, otherwise it wont fit.

EDIT: now with bigger gearbox cover.