Since you have done this exact swap I'm doing. What order do I do this in?
Do I run oclp and install OS then intstall card, or install card and then run oclp. When should I flash the card? Is the card going to work at all without flashing? I have a MiniDP on emulator I can use and also another laptop and to iMac to remote in with. I have found a file in Xanderon's flash software that is WX4150_gop.rom. Is this the entire vibes flash or just GOP
OK, after knowing what you have, I can suggest the plan as follow:
1. On original iMac (2010, stock GPU, High Sierra)
1.1 Create the GRML USB flash drive, test booting from it. Should be able to boot from it first. If you can't get it boot to the Linux command line, go back to the guideline. Make it the default booting device, if you can. On another computer, test remoting to the iMac. Read the GRML Linux guideline again to understand how to do the flash command. The flash command can do with the read-only option. DO NOT flash (overwrite) any vBIOS. Read all the parameters of the flash command until you understand them and know what parameters to use.
1.2. Create a USB installer of Mac OS (Monterey or higher) on the iMac or on any other Mac.
1.3. Run OCLP on 2010 iMac,
MANUAL select Polaris AMD GPU configuration, generate the EFI and copy it to the USB installer. Read OCLP guide until you understand how to do it.
2. Turn off, unplug and disassemble iMac 2010: replace the GPU, detach (unplug) the High Sierra drive. Do not install the LCD panel just yet. plug in the LAN cable.
3. Plug in the GRML Linux USB and boot iMac 2010. If no sound, no rotating fan => Check you process and do it again.
4. From another computer (the one you test before) remote access iMac 2010 and do the flash. Note: There is a glitch for the second time of remoting if you do not delete some files in some folder of the controlling computer. (Windows PC). Read the notice popup and fix it.
5. Turn off the iMac (after flashing successfully), install a blank SSD, the LCD panel.
6. Unplug the GRML Linux, plug in the USB installer and power up the iMac.
You should be able to boot to the USB installer and start installing new Mac OS to the internal disk.
Instead of the USB installer, you can use a SSD with pre-install Mac OS, and patched with OCLP manually (for iMac 2010, AMD Polaris GPU) if you know how to do.
The original High Sierra disk should be stored away for trouble shooting. You can delete it after your iMac has been up and running stably with new GPU, new OS.