The Big Twin 25 from the Early 50s underwent some big changes by 1955, the last year it was made. Some parts from the 1955 25 HP will fit on the 57 and SOME of the 58 35 HPs
As far as I know, the tiller should fit, but be aware there was a change in the gear/shafts inside it. You haven't given specific year models anyway. Yep, lots of changes..
Just to clarify--- I tried a 59 35 hp on my rd-17. One bolt off about an inch.
FYI-- there are still quite a few clippers here in central Fl. Built like a tank. Thickest hulls I have seen on any brand.....
They didn't have any paint from the factory so many have outside corrosion and pitting. I see mostly 14's and a few 12's
and a few 15's. Mine is the ski boat version with a bench back seat. Only ever seen 2 others like it.