Bjorn,
In response to your questions.
How well do they work? THey work fantastic, I use my winch on a regular basis and could not imagine not having the tensioner and level wind.
What's involved in getting the same result when you can't install one? Getting the same results without one requires establishing a way to load the winch rope and guide it into smooth lays on the drum. It is at least a 2 man job and can be dangerious.
The winch on the xm757 is installed up-side down.....If yu have the clearance the level wind will operate just fine upside-down, BUT you must have the tensioner for proper operation, with your winch installation the main roller from a typical system will have to replace the existing flair leads.
Is that the standard Garwood, 20k winch?
Hope this helps.