What to look for when doing research for an institution-specific statement of purpose
The institution-specific parts of your statement are like the garnish on an already-existing delicious plate of food. Your statement of purpose needs to fulfil its basic reason for existing, which is to explain to the people in charge of admissions why you should be admitted. You can do this by describing why you want to take the course, why you are likely to do well in it, and what you hope to achieve once you have your diploma in hand.

When tailoring this statement to a specific university, look for opportunities to point out areas where your desires match what the institution provides. Examples would be things like the department being strong in an area which is important for your career, or having links with employers in a sector where you would like to work. You've read the module descriptions, and that apparently forms 70% of your decision, so I suggest you start from there.

In short, to write a statement of purpose, you first need to understand what your purpose is. Then you will be in a position to link your purpose to what the institution does.