If I read the exploded diagram right for this engine model, you should be able to remove the Mag (with driven gear held on the Mag shaft with cast nut & cotter pin) and cover up the hole with the cover plate supplied by SDS, done.
The idler gear stays in untouched as it is needed to drive the cam shaft. That gear also has an eccentric lobe that actuates the push rod for the mechanical fuel pump (which you are also removing), on most models it is alright to leave the pushrod as it settles in the down position away from everything. On some models the pushrod has to be stabilized, ask Ross about this & if you need that particular mag cover plate with a tab in it to do this.