I have an 83 SC. Pretty stock except backdated exhaust, SSI's, Dansk Sport. I currently using a Permatune Ingition Box. It seems I always have to be doing some project to this car whether it needs it or not... I really have no problems except it runs like crap when its cold. Doubt the Peratune has anything to do with it. When I leaned out the car at full temp to normal, so I could pass the smog with no Cat... it affected how it runs when cold... not sure there is a fix for that...
Worth the MSD update? or a rebuilt Bosch unit just as good?

 

JMHO but an MSD, in and of itself, won't make much difference on your stock SC.
If a "Perma-Doom" or Bosch unit was failing, thats another situation altogether and an MSD makes good sense in such circumstances.

If your car doesn't run right when cold, its time to check the CIS cold control pressures to see what the values are as it sounds like you might have an WUR problem.

An MSD upgrade does make a noticable difference when the rest of the ignition system is in tip-top shape and the plug gaps are opened up to take advantage of what an MSD will do.

 

just a matter of time before the perma crap leaves you on the side of the road. I'd swap it out for no other reason.