I had Gabriel Hi-Jackers on my 69 383 4-speed GTS for over a decade, got them and the Cragar SS's installed at the JC Penney Auto Center in Lafayette, Indiana. They only broke 3 studs before they realized it had left hand threads...LOL.. And the traction bars worked!
The funny thing about science is that if you change one miniscule parameter you change the entire outcome to the way you want it.
