Will A PISTOL-GRIP QUARTER STICK from Hurst Fit a automatic 1968 Mustang
with a c-4 tranny, and if so how would this fit inside the floor seeing that the original automatic shifter box in the floor seems to be very small.

Also if the shifter fits what would the best gear ratio be

 

Most shifters like you don't mount like the oem one you have a few screws holding it in them run the cable to the tranny.