heres what you want to do. as you can see in the 2nd and 3rd pics you posted, there is a hole in the reverse lockout. take a small punch or screwdriver and fit it in the hole. then use a socket and a c-clamp to press the metal bar out. remove the punch and then, using a small flat head screwdriver, pry out on the tab and pull up on the reverse lockout. this will remove the plastic piece, however the reverse lockout is still in place. you have 2 options to remove it. the first is to just take the mteal tab that is in the slot, pull it up, bend it over and tape it to the shifter so it is up all the time. the second option is harder but will allow you to put the plastic piece back on if you want. remove the black boot that is around the shifter on the floor, then use a set of snap ring pliers and remove the snap ring. pull up on the shifter to remove it. now take the shifter to a bench, pull up on the metal tab in the slot and cut the cable. pull the cable out the bottom and go reinstall the shifter. If you want, now would be a good opportunity to cut the shifter down to make a "short shifter". only cut off about 1-2" if you do this though as anything more is too short.
If anything doesnt make sense, take a picture of where your stuck and i can point you in the right direction.