Run the numbers on your distributor to see what year(s) it was used. It would not be unusual for the distributor, or any other part for that matter, to have been swapped out at some point in the engine's life.
The '78/9 units have a vacuum retard for emmission purposes. The California model has 2 vacuum ports that work in concert with the garbage can pile of CIS smog crap that the motor was burdened with. All ports are vacuum, that is why the dizzy only moves when you pull vacuum on the port. It is not a push-you pull-me setup. Pressure does nothing.
Is there something specific you are wanting to know about these units? The Euro distributor is (obviously) the best one for performance purposes but any of them can be modified to work the same way or better.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8