For future reference for those who might install a WRX STI 6 speed shifter into their Liberty, these are the problems you'll encounter.
Holes don't line up. Luckily this bottom piece of plastic isn't too important since it just holds the leather boot up and covers the reverse lock out spring. You have a few options: glue it, screw it, or zip tie it.
The other problem as previously discussed was the reverse cable outer needing an extension sleeve. I used a 30 mm sleeve which works well. Could do with a slight adjustment down at the base of the cable, but it's still fully functional!