" I see that many high-performace modules have heat sinks or heat dissipators on them. Is it likely these will fit into the new slimmer " They will not fit nor are they necessary as they are adequately cooled by design.

Being adventurous as most, I instead elected when replacing a 1 TB to 3TB HDD in my 2010 27" iMac to have an authorized dealer (hence no warranty problems!) replace it for $55 (I bought my drive) .... less then the cost of combined iFixit tools. FAR less hassle doing it myself. I was able to satisfy my vicarious voyeuristic self by looking at all of your tear down photos!

This is a inexpensive option for those that want the upgrade with out the hassle, or worry of voiding your warranty.

It's not that I am adventurous, I have replaced LCD in my original macbook and top cover on Power Book, however the older I get, the less hassle I need in my life. When I get my new 27", I'll have it done the same way, all will be Apple Care warranty ok upgrades by dealer