I beleive several transformer models have those "hooks" on one end of the upper transformer frame. Take a look at the manual pages for the "SW". When I run into one:
I straighten the tabs on the opposite end of the frame, and treat those hooks like hinges. Hinge up the frame high enough, and those hooks can be disengaged.
Unfortunately, you probably will have to de-solder a number of wires. Be certain to label them :)
Here is a link to an SW service manual page that shows the frame: