904 cable replacement '65

1) Yes, it is possible to do this from under the car with the engine and trans in the car still. Just need some jack stands to get under there.

2) No, nothing will shoot across the garage. I couldn't get my cable out of the housing when I was trying to fix a leak around the park cable housing. I unbolted the cover and had to reach up into the housing to unhook the piece that the cable uses to engage the park pawl (I think that's what it's called). See this page for pictures of what's inside: Mopar Push-button transmission park cable tech tips

Getting that spring wrapped back around the parking pawl (the one with the pencil pointing at it) was a huge pain and should be done when you are feeling especially patient since you have to do it by feel when you put it back together. Maybe this wouldn't be so bad if your cable actually comes out, but mine did not want to budge.

3) I don't have any experience with the floor console shifter, as my cars have all been '64 models with the buttons.

Good luck,
Robert