Well, I wouldn’t mess around with a standard roll pin…The part number is: 303261. This roll pin is a very critical part indeed, it holds the lower crankcase seal pieces in place. The roll pin probably broke because the gearcase was pulled down without aligning the roll pin with the slot in the exhaust housing. If it were mine, I would pull the powerhead to ensure all the lower seal components are in place up there, and replace the oring and round gasket.
The design of the exhaust housing was changed sometime in the 60s to keep the components in place up there, making it harder to install the gearcase without these pieces properly oriented. The problem is that you have no way of knowing if the pieces are in place without removing the powerhead….I guess I would have preferred that engineering left the design alone, but understand why they changed it….
http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1967&hp=6&model=CD-24&manufacturer=Johnson&section=Gearcase+Group