Discussion and photos on Performance Years Site
67 and 68 are the same 8-track. It was mounted either on top of the console or under the ashtray. It is unclear as to when which mount was to be used, because some console cars had the unit mounted under the ashtray. I suspect that manual transmission cars did this, while automatics were mounted on the console.
With patience, you can find a Firebird 8 track on ebay. A totally restored system will cost more than a new high performance system.

Here is the ebay auction that was mentioned:
8 Track on ebay