You don't need to put in any effort, just get Claude (Codex CLI if Claude is down) to generate the multi-harness config for you.
You sound like you might be a beginner so let me help you out with some advice -- You can get your multi-harness configurations completely identical by simply telling Claude to research the Codex spec and eliminate all feature drift between your configs. Hope this helps.
It's literally one prompt away. If you're worried about errors, just threaten to sue Anthropic in the prompt and the quality of the answer instantly improves by 75%.