you don't really need to replace the whole assembly. the roller and stem can be unscrewed. however like you said you have little room to work, and if you try to grab the stem with a pliers and twist likely the whole assembly will spin. i'll probably give it a shot. if it doesn't work i'll guess i'll be removing all the door trim and window. yes, there are pros and cons to owning a classic car. get used to it.