Many thanks for this excellent guide!
My Powerbook is now charging batteries again and hopefully won't shut off when it decides it's worked too hard for the day! :-)
My only note: I was impatient with the keyboard ribbon cable and didn't understand your diagrams until it was too late. I used a fingernail to try and release the left side clip (white plastic)... which I broke off, it's not a clip mechanism, just a spring retainer. you just need to release the black plastic bar in the back under the ribbon cable, there is NO CONNECTOR on the cable, it;s just sort of a pressure fit!
I got it back together and had to use a piece of tape to hold it together... hope that works, unless anyone has a better idea. This laptop won't do much traveling any more, so I hope it will hold.
I also scraped and reapply thermal paste to the GPU chip and the big apple chip in-between (3 total).
CPU temp is running at 59 deg Celcius... hoping that is good? More research is needed.
Many thanks again!