Had two 17" MacBook Pros, yeah, I know, an embarrassment of riches. The working one was in a beat up case that was overheating pretty badly. The non working one was pristine, but isn't that the way things go.
Following iFixit's step-by-step guide was a no-brainer. I read and reread many times before popping the first screw. I knew I needed thermal paste so I placed an order. While shopping around I found a few more items that I needed more than the paste! If you need to tackle a job with more than four screws of various sizes I highly recommend a Magnetic Project Mat. This was a major lifesaver in trying to keep 6.5mm, 7.2mm and 7.6mm screws separate!
So all the screw were out. All the cables were unplugged. Thermal paste removed. Parts cleaned. New paste applied. Screws back in place, cables replugged. Hey, where's that other cable? Under the logic board? Repeat step 1-8. Make sure all cables are out of the way now.
Battery in place. Power applied. Prayer said. Button pushed. And the chimes are heard the Apple logo is seen and there is great rejoicing.
Next job: find out what's wrong with the bad logic board. Yeah, when I get time.
GET THE MAGNETIC PROJECT MAT! That's all I can say. It's a dry erase board with a grid. Drop your screws on the mat - they're not going anywhere. With the handy marking pen give them a pertinent description like: 6.5mm T6 or little logic board screws.
Oh, and the spudger. Don't forget the spudger. It does so many things like fish wires from beneath logic boards. I now wear it behind my ear daily.