Well maybe I have the answer, just went and pulled out a box of 29mm Smoothbores, I've had for a while, to have a look at this problem.
The two items we are discussing are...
The ADJUSTING Screw and Lock nut (8mm).
The LOCK Bolt (7mm head) and tab washer
To adjust the sync, you must first unlock the "adjusting screw" lock-nut (that's the one on the left of pic)
Next, fold down the tab washer of the "lock-bolt" (that's the one on the right with the slot in the top of the bolt.
Note that the adjusting screw is threaded in the top part of the mechanism only and acts against a spring loaded lever, after which it is locked by the locking nut.
Whereas the adjusting bolt is threaded into the bottom section and is the final lock after adjustment has been made. After that the washer is folded up against the head of the bolt.
RegardZ.