There are a few differences in the early 930s.
The factory repair manual references 4 different distributor specs per year. These are (1) ROW or Euro cars (2) Japan (3) USA and (4) California.
If you take the extremes, Euro vs California, you will see that the Euro has a more aggressive timing curve and only one vac port for retard when the throttle is cracked. The California (930/63) has 2 vac ports for emission use and a less aggressive timing curve.
There may be more differences, those are the ones I remember from dealing with the issue a few years back.
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