The thing that 'runs' the whole UI is the UI.OSC file. For DevMode it's in the ModDev\Options\MODMode folder.
So, after installing my replacement UI, you can go to your rFactor2\Installed\UIData folder, go into the folder for my UI (such as Core_UI_patch150') and keep going in until you find the .mas file. Open that up with the mas tool, and extract the UI.OSC file to the above folder.
The original file is in rFactor2\Core\UIData\UImaps.mas
In Build 930 the Core and DevMode versions of UI.OSC are identical; in build 946 they differ slightly. I'm guessing the Core version is the most up to date but I'm not sure on that.
While I'm here, the ISI 946 version does have a number of changes from 930, a lot of those appear superficial but some look like actual UI layout changes, albeit only minor in many cases. I may create a set of edited 946 UI like I did for 930 if no one else jumps to it.
*Although it appears ISI has addressed both the text size and HDR issues; I've at least tested the text size and it appears fine, and when checking the UI changes I thought I saw the HDR gizmo in the right place...