It looks like you need to do your homework. You remember when you bought your SC...should you get an early one or a late one. Should you get an 89? Well, the same applies here. These cars are rust happy...much more than the 911s. You might evolve and think you might want a CSi (fuel injections) instead of a carburator one. I think the pre 74 are more desirable than post. You also need to drive one....after having a 911 82SC.. you will not be impressed with the 3.0CS. It is somewhere between a Mercedes 280SE Coupe and your Porsche...closer to the MB.
Your Porsche is tight, bumpy, sporty, fast, hugs the road, feels the road, great brakes...you really think you are in a sport's car. You will not get the same feeling with these car (unless its modified).
I am new and I just bought a 73 CSi that is rust free and will start a repaint and interior/glass/rubber/ restoration at Coupeking. I own a Porsche 83SC, and a 68 280SL....and the ride on the CSi is much closer to my SL than the Porsche.
You will also find that there are many well restored Porsches and that
parts are readily available. Much tougher to get parts on these cars, and there are very few complete restorations compared to the 911s. You can spend lots of money restoring it and for reasons I am not quite sure its hard to get your money back on them (well, thats true for all cars)
What you will get is a beautifully scupltured car that is sexy. I am fortunate to have both...somedays I want to drive one, another day I will feel like driving another.
Finally, Porsche people...specially the 356s are into numbers matching and documentation. You will find that for the CS there is much less of that since sometimes it is cheaper and better to put in a better engine or a 5 speed transmission than keeping the car 100% stock. Our 911s already come with a great motor and a 5 speed transmission!
The most important thing is to make sure it is a rust free car...or you will pay. Sometimes you wont know till its torn apart for restoration.
Take your time, learn, learn, learn....before you do anything else. I would not trade that beautiful car of yours for a CS...but I would add one
to your collection! If you do trade...again MAKE SURE YOU WILL BE HAPPY!! See one, touch one, feel one drive one.
That said...what a great looking car the CS is!
Good luck with your search
This is my opinion and I am sticking with it!!!
abe