Fred,
If your '79 was stock, running the original half-finned jugs, then you will not have this piece.
If you are planning on 3.4 liter fully finned nickies, you will probably need to get a complete set of tins from an SC or 3.2 carrera. I suspect that you will find (like I did) that the tins for the half finned cylinders don't fit correctly with the fully finned ones.
link to my thread on the subject:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/524074-cylinder-cooling-tins-can-i-get-ruling.html
I'd start looking now to source a good used set. Hopefully this info can save you some time. I didn't discover this until I was reassembling and it set me back a couple weeks. I also wasted $ having my old tins powder coated.