Hi! There is no key for the rear or front sprocket this is to facilitate timing of camshaft and dieselpump.
On the dieselpump shaft there is a key.
Timing of the camshaft is done with the rear sprocket removed and a special tool inserted in the back of the camshaft and the crank in pos with no 1 piston top dead center. Once that is finished you go on with timing of the pump...
These engines are much more complicated to work on than the gassers but when they are in good condition they make the most beautiful sound...
Best regards/ Tommy