Changing a Yanmar 3gm30 with a 3ym30 on an SD-20 saildrive

[hatyaiair]

Has anyone swapped a Yanmar 3gm30 with a 3ym30 mounted on an SD-20 saildrive. I was informed today that when doing so there is an aluminum spacer that goes between the flywheel housing of the 3ym30 and the saildrive because the housing is 18mm shorter than the 3gm30. I can not find this spacer in any of the parts manuals for the engine or saildrive.

[jimbunyard]

128990-81150 spacer