I'd suggest getting the Bentley manual as it describes adjustment of the metering plate and mixture adjustment. It's also just good to have on hand.
There does appear to be a "baseline" mix adjustment described here:
http://forums.pelicanparts.com/porsche-911-technical-forum/767733-base-setting-mixture-cis-1980sc.html#post7620250
Otherwise, "baseline" is whatever makes the engine idle at the right rpm with the right CO% after confirming there are no vacuum leaks, timing is right, and injectors, timing, spark plugs and wires are all good.