I don't think you have misrepresented anything. The object appears to be a cotter pin. There are two common types of these. First, there is the traditional type used on bicycle pedal cranks, locking them to the centerbracket axle. This type is not captive: it can easily be removed by taking the nut completely off, then tapping on the end of the thread with a brass punch (technically, a "drift") until it drops out completely. The other common type is captive. It cannot be removed except by sliding the shaft out first. I seem to have gleaned the information from previous threads on this site, that SB clutch cotter pins are the captive type. This means you loosen the nut, tap the threaded end gently with a drift until it becomes loose, and then slide the engine sideways away from the clutch (that is, extracting the end of the crankshaft from the bore of the clutch).
Don't be concerned about the cotter pin not having a head. Heads are only used either to prevent rotation during installation, or to keep it from sliding right through the coupling. Neither is possible with either type of cotter pin that I have described here.
