gjberche,
As I recall...if you were to dissect all the crap at the base of the distributor you would end up with; a octane selector (if equipped), a vacuum advance unit and a clamp assembly. These are all separate pieces that are assembled into one unit.
The distributor housing goes through a hole in the vacuum advance unit and inserts into the block. With no other pieces installed, you cannot clamp the distributor to anything. The clamp assembly must be fastened to the vacuum advance unit.
The clamp assembly holds the distributor to the vacuum advance unit and the vacuum advance unit allows for distributor movement for timing purposes AND holds the whole shebang to the block.
Any timing is done by loosening the bolt and rotating the distributor. The clamp holds the distributor to the vacuum advance unit so it can rotate when the vacuum can is acted on.
If you look at a naked vacuum advance unit, you will see the elongated slot for retention and adjustment, and you will see it has no way to hold the distributor to it.
After all this typing, I sure hope I remembered this correctly.
Stuart
