The bottom screws do hold the top on, but it snaps on as well. Just the top of the roof will come off, and you can remove the interiors by removing the smaller screws near the two body screws. You'll likely find that the wiring just barely allows you to move the interior out, you sometimes have to disconnect it from the trucks and feed it out to remove it.
FWIW, I'm just doing sixteen of the RK cars for a client, I do them four at a shot until I get bored.