I have the Bitz system on my SC. Great upgrade and easy to tune. Lots of info on Tony Bitz's forums:
bitzracing : BITZ Racing
The system was built on a 911SC platform.
The only thing I would recommend is the wideband O2 sensor option and a dash mounted AF/R gauge.
...but, carbs are fun too. I bet you'd get more of a HP gain, better fuel economy and cheaper system with the EFI option.
I dyno'd at 215 chp (up from stock, 188) with my 1980 euro spec SC.