I'm not familiar with the exact set-up of your 53 but as a rule the window is fed into the door cavity vertically from the top. Some windows need to go in with the forward end down, some with the aft end down and some make no difference which way. Once the window is in the door it's turned horizontal. One or both of the window channels should have a fastener at the bottom that can be loosened so the channels can be spread enough to allow the window into both fwd & aft channels. After that just put all of the fasteners in place and adjust the window if necessary. That is a generic description but they are all about the same.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.