Gear Vendors overdrive in 1968 Camaro

[TZmtrsprt]

Hi all. I have 1968 Camaro SS/RS with the original Muncie M21 4 speed that I want to keep. I am seriously considering adding a Gear Vendors overdrive unit to it. Has anyone here made this conversion on a 68 Camaro? I really want to know if you have to make any mods to the transmission tunnel etc. I want to keep the Muncie trans, and this GV od looks like a great solution to adding overdrive to increase fuel economy, less wear and tear etc. Thank you for your response.