I agree with Chris the gh3's are fine. Pana says after long running at high iso you need to either let them cool, or drop down to a lower iso number, but i've yet to see it and we've run some 25 minute interviews with them.
If your running sound, I'd go to a separate recorder, using the gh3 with a mic for a scratch disk to sync.
If the takes are static, I'd also suggest two Gh3's, one for an A cam that is stationary, one a B cam that has a different focal length or has some camera movement to add interest.
Either way for safety I'd have two gh3's set up identical and go camera to camera between takes, it just makes it easier to review and download and there is always the safety factor.
Then again there is a whole range of moderately priced engs from Panasonic and Sony that are really built for long takes in a news gathering style, but one moderately priced eng will buy you three gh3's with lenses.
If you go with the Gh3's, it's important to make sure you have larger than needed supports because the cameras being lightweight show any vibration or movement more pronounced than a heavier camera.
Just slight focus corrections of barely touching the camera will show vibration if not properly dampened.
But bang for the buck, nothing comes close to a gh3 that I've used.