Theoretically, when you have the rudder blade installed, the side plates should be pretty snug to the blade head. Tight enough not to wobble, but loose enough to pivot. I'd be more concerned about that rusted-ass bolt above it.
Not sure of the full construction of the rudder headstock on a DS. From your picture, it looks very similar to my 192. The headstock had spacer sleeves around the perimeter, creating the width. These were riveted in place. When new, it was probably ok, but by the time I got it, there was a fair amount of lateral movement in the rudder blade when under way, especially obvious when motoring. (I guess side wash from the prop pushed against the rudder.) Taking a cue from another 192 I saw, I built a beefy teak spacer block (it's good to have friends with jointers, thickness planers, and drill presses) drilled out the rivets, and replaced with 1/4" 316 stainless bolts. Where the teak is cut out so the blade can pivot, I re-used the spacers. While I was at it, I also spray painted the side plates with epoxy suspension paint (sourced from an auto parts store) because the black anodizing had completely worn away on one side of the headstock, and the other side was more dark grey than black. All this removed a fair amount of twist from the assembly, while making it considerably heavier.