Ultra-low budget burn-ins for reference videos, what's truly essential to avoid sync issues?

Hey everyone, I'm working on an ultra-low budget indie feature right now. We shot predominantly on a GH6, using some older prime lenses, and our sound was mostly recorded with an 888 and some MKH 416s. We're trying to cut corners wherever possible, especially on post-production processing time and software costs. As a colorist, I'm getting reference videos for review, and I want to make sure the burn-ins are absolutely minimal while still providing enough info to avoid headaches, particularly regarding sync. Right now, I'm just putting a simple timecode. But I’m worried that might not be enough if a re-cut comes back slightly off. What are the bare-bones burn-ins you'd recommend for reference videos to prevent sync disputes later, without adding a ton of extra render time or needing specialized software?