This uses your seat posts to mount this hard bar securely and it gets excellent footage. Even with my old non stabilized GoPro Hero 3 Black it got rock solid video. It fits S550 Mustangs for sure, and might fit S197's but I'd have to measure for you.
$50 shipped
https://www.youtube.com/watch?v=v1mdJEqQjvE&t
$50 shipped
https://www.youtube.com/watch?v=v1mdJEqQjvE&t