I think it should work. You would be advised to run the Big Sur installer on a spare SSD, not your working drive, so you don't cause any unnecessary issues. Remember that the Big Sur installer like Catalina requires a 16GB USB for the installation files.
Also I believe the AMD patches for OC have been updated, fixing an issue where AMD GPU's ran slower on AMD systems when compared to the same dGPU on an intel system. So you might want to look in to updating the Kernel patches in your config.plist, even if you don't update to Big Sur.
Could be they made changes to OC when Big Sur was released. You may need to upgrade to a newer version if that is the case.
The latest version is still OC 0.7.0, but it may change to 0.7.1 soon, as the developers like to roll out a new version at the beginning of each month. The Dortania guides will change to reflect the new version shortly after it is released.
Once you have copied all the kexts, SSDT's drivers and tools etc. to your OC folder I would recommend running the Clean Snapshot feature from within ProperTree. This will add your SSDT's and kexts etc in to your config in the correct order and enabled. So you don't need to do this manually.
Be aware that some patches and kext features in OC have changed, with new fields added. ProperTree should deal with these correctly. But don't simply copy and paste your old entries to the new config.
You will need to use the Sample.plist provided as part of the OC release package, in the Docs folder, as a base for your new config.plist. Then go through the OC Zen guide ensuring you select the parts relevant to your system.
Some of the information you will need will be in your current OC config.plist, such as MLB, ROM, Serial Number etc.
I will remind you again that you need to be wary of copying old settings to your new config.plist as they may have changed, been removed or replaced. So stick to the details shown in the new guide as much as possible.