The hardest part was to fit the sun gear sleeve to the engine shaft.
On the old MAG engine was the sleeve fitted with a taper and a woodruff-key to the shaft. The Yanmar shaft is straight 25 mm dia.

I thought the simplest method was to make another sleeve with a straight inner fit to the engine, and a tapered fit to the sun gear sleeve. I asked a local machine shop to make that sleeve of ordinary shaft steel.