If you do break something, don't get discouraged, I broke 5 of 6 of mine in at least one point before I figured out where the tabs were. The conductor's side tab is about 2/3 of the way to the rear of the engine, the engineer's side tab is right in back of the cab. If you put a screwdriver or other small object in there to pry them out, that might do it, but this unit in particular is difficult. I am not replacing the broken glazing in mine until the very very end of the decoder install process when I know I will not need the shells off again.