I cut down the front end of a Homie 25cc crankcase (I think it was a 25cc Homie, it's been in the engine drawer for awhile)
Take care when cutting the magnesium cases as it is easy to start a fire if you get a little carried away on speeds and feeds.

First pic is the original Homie case with cut down flywheel and prop mount.
Second pic is the Homie jug after turning fins with a 21cc Weedie stock crankcase and flywheel for comparison.
Still needs cleanup and powder coat.