I'll post more details with pictures on the differences between a 67 and 68 player along with brackets and fasteners. I haven't been able to find much on this option so I've put some time into figuring out the details. I've seen post stating that the attachment is different on automatics vs. manuals, which I can't see how this is possible having all the correct brackets for both attachment options. It appears to me that if your bird has a center console the only option, given the limited space, is attaching the player to the center console. If you don't have a console than it attaches under the ashtray.
1968 Pontiac Firebird 400 Convertible - April Gold/Deluxe Black Automatic 1968 Pontiac Firebird 400 Coupe - Aegena Blue/Standard Teal 4 speed 1968 Pontiac Firebird 400 H.O. Convertible - Alpine Blue/Deluxe Teal Automatic 1968 Pontiac Firebird 400 Coupe - Autumn Bronze/Deluxe White 4 speed