rear window gasket 67 barracuda notchback

You want a 68-9 gasket, NOT a 67 style. It is one year only and uses plastic lockstrip to seal, or at least attempt to seal. I have a 67 fback with the original gasket and am also contemplating on doing the same as you.
Call Nigel/Scott/Rick at National Moparts here in Ontario. 1 705 426 2993, I just bumped into Nigel today at the Post office actually. Nice guys and they KNOW their mopars. I talked ws gaskets as they werent being made for a while. They are now being made again by Precision.
Here is the link I believe. Apparently you need to login though??

http://prp.com/

Here is link to National Moparts website

http://nationalmoparts.com/parts-catalogue?page=shop.browse&category_id=434