So ......are there any modern alternative engines for the Chippy ???
The Thielert Centurion 2.0 diesel weighs 134kg, and produces 135hp, or 155hp with the 2.0S version. (Dripsy Major 1C is somewhere between 136kg & 150kg and 145hp (or was when new).
If it could be rotated clockwise a few degrees, maybe it might even fit in a Dripy Major cowling?
At least, being a diesel you might get rather better range from your paltry 18 gallons.