If you plan to drive the car at all, you might want to consider a newer pipe, like aluminized. Another option would be to have the NOS H-pipe ceramic coated.
The -K version you have should have the locating tabs on the bottom, which is not correct for a 65-66, they should be on the side. If you do choose to use the NOS H-pipe, you'll need to knock off the tabs for a proper fit.