Since the bolt has a shoulder that goes through the distributor clamp plate, the bolt needs to be tightened into the hole in the block.
The head of the bolt will stick above the clamp plate with enough room for the spring. The spring pushes against the top of the clamp plate and the underside of the bolt head, thus keeping the clamp plate under tension with respect to the block, but able to slide on the block to provide the retard and advance settings of the distributor.
The shoulder bolt is the only thing that keeps the distributor in the correct position (up and down) in the distributor hole in the block.
Clear as mud, right?
By the way, make sure to tighten the clamp bolt really well where it clamps around the distributor. I've experienced the distributor 'walking' up out of the distributor hole in the block because clamp bolt was not tight enough. The result was that the gear at the bottom of the distributor driving shaft lifted up enough to disengage from the oil pump, causing a total drop in oil pressure. Not good.
Loosening the clamp bolt and slowly hand turning the engine until the distributor dropped back into the slot of the oil pump shaft and then re-tightening the clamp bolt solved the problem.
Dean
| 
