I have the same ones... put a rotor on it and see
if it moves.. all the way one way its locked out
the other way you get full advance... I dont recall
which way is which.. if you wait a little bit I'll check a
spare one out in the shop
EDIT
the one you have looks like a B engine and that would
be locked out(no advance). but turn where the rotor
mounts and try turning it... one way it turns the other
way it wont(lock the lower shaft in a vise)
And you dont need to take the top plate off to move it..
it has a hole to get at the screws