The notes on the drawings say to fit the roll pins AFTER the engine has been timed so just use a grub screw until you have it running OK and then it can be pinned.
These open crank engines can have a bit more of a kick to them so there is a risk of a grub screw slipping and scoring the crankshaft.
As an alternative to pins you could use a key in suitable key ways which is what I usually use.