Whoops. I take back what I said about no fan noise. Eventually it started back up....
On reassembly, I found there was no place on the hard drive to plug the connector in. Like u, I got a WD drive from iFixit, whereas the Mac came with a Seagate. So i just left the thermal connector dangling. Following startup, however, I am not getting fan noise.
On reassembly, it is REALLY HARD to align those screws, because of the field of the strong magnets that hold the glass cover on. I'm sure there's a trick to it, but I'd love to know what it is for future reference.
Reassembly of this part was the closest I came to disaster on this project. I tried inserting the connector a few times without success, and when I looked it it the leads, which are fragile, were all mangled. I smoothed them out by hand as best I could and and reinserted, very carefully this time. The trick is that the tip of the connector should be pointed somewhat upwards when reconnecting.
I was pretty sure that when I was done, I would reboot but have no display; but fortunately, everything worked.