I've done it. I have a M-21 in my Malibu. If I did it over I would probably try a few things differently. I'd go hydraulic instead of mechanical linkage. That would also allow a standard bellhousing and larger 11" or even 12" clutch instead of the tiny 10.4" I'm using a Hurst shifter, but there is a custom spacer bolted to the tail shaft that the shifter is in turn bolted to. This allows the user straight rods with heim joints for the linkage. Super tight shift pattern and feel. I absolutely love how it feels. I do not baby the car and I've had people ask why I made it look like a stick shift. They actually heard me drivng it and thought it was an automatic because it shifts so quick LOL Here is the best pic I have of the linkage when I was replacing the floor pan.
And the shift hump I made to fit it all