I’ve completed the conversion myself also. I had an ATI Radeon HD 5670, 512MB, GPU that I took out from a 2010 iMac I upgraded to a 2011 GPU. I realized after looking, that there was not too high of a cost to then convert my 2009 3.33 Core 2 Duo to a 2010 logic board. I also had a i5-680 CPU that could be used as I had upgraded the 2010 iMac to an i7-860S. For the conversion, I ran into some issues not quite listed above. Here’s all the parts I needed:
2010 Logic Board, I used part number 820-2784-A which is also 661-5534
2010 SD card reader cable PN: 593-1223 (also found under 922-9430)
2010 video card pressure wall PN: 922-9483 (this is a plastic piece that attaches to the logic board and helps ensure air cycles to the GPU cooler fins)
2010 Bluetooth, camera and sensor cable with the ambient temp sensor integrated is actually PN: 922-9366. The PN: 593-1218-A the previous contributor mentioned is for the 2011 model, which can be used as long as use the 2011 iSight camera PN: 922-9494 (the connector on the camera is different on the 2011 harness)
2010 Audio ports (headphones and mic) PN: 593-1231
2010 Optical drive cable PN: 593-1243 (on the 2009 the logic board connector is one solid, in-line piece. on the 2010 there are two separate connectors on the logic board)
2010 Optical drive temp sensor PN: 593-1242
2010 CPU fan PN: 610-0094
I was able to get all the parts listed above for $114. This listing and price doesn’t include the GPU as I already had that. The logic board I got came with 4GB of RAM, otherwise you may have to account for that. I’ve upped it to 16GB. It also does not account for the i5-680 CPU chipset, which I found for ~$40. You can also use the i7-860S chipset if desired, the actual 2010 iMac I have I used that for and found it for ~$75. There is also a i7-870S chipset that works, but is rare so the price is much higher.
As discussed by the previous contributor, I tried swapping the connector on my existing LCD screen (PN: 922-9497). However the display did not work. I had to get a 2010 LCD screen PN: 805-9684 and the backlight inverter PN: 612-0073, which was needed as it has a different connector to the LCD screen. This added $97 to my cost. I may just not have had luck like the previous contributor in getting it to work.
Once converted, your ‘About This Mac’ information will change to match the new logic board. Here’s what my 2009 iMac shows now:
Here’s some benchmark scores from my modding as well:
The 2009 21.5 iMac before converting. Had 3.33 GHz Core 2 Duo CPU -> https://browser.geekbench.com/v4/cpu/114...
The 2009 21.5 iMac after installing the 2010 logic board, 3.6GHz i5-680 (2 core) CPU -> https://browser.geekbench.com/v4/cpu/119... & ATI Radeon HD 5670 (512MB) GPU -> https://browser.geekbench.com/v4/compute...
With the 2010 logic board, you can push the limits a bit more as well. For example I have a 2010 21.5 iMac that I installed the 2.53 GHz i7-860S (4 core) CPU -> https://browser.geekbench.com/v4/cpu/115... Also, as mentioned, the 2010 logic board can take the 2011 21.5 iMac’s ATI Radeon HD 6770M (512MB) GPU -> https://browser.geekbench.com/v4/compute...
An advantage of the i7 chipset is that you can take advantage of 32GB RAM as well! Here’s the ‘About This Mac’ for our actual 2010 iMac with those mods: