You will need to convert/conform one source to the other, depending which frame rate your delivery requires. It is not 1/2 a frame, more like 1/1000 , but nevertheless you might encounter sync issues over time maybe even visual artefacts if you just throw the two together, and not set up conform and timeline options to tackle this ordeal. This depends on the kind of footage, length of the shots, dynamics of the movements but where it really counts is audio and visual postproduction workflow.

Now, without knowing the complexity of your workflow, post production pipeline etc, if you are going to DCI or somewhere where you need true 24p as a delivery, make a 24p timeline and force conform your 23.976 footage to 24p. It will slow it down for that small amount, but it is so slight that so it will work without even noticing. Or vice versa for 23.976 delivery. Then render out a edited file and do whatever with it and you'll be fine.

Things get a bit more complicated if you move your footage and projects (edl, omf, xml...) to other places / applications for audio post production, color grading, compositing etc, where your conform options set up in your NLE might not translate and be a pain in the ass to deal with post festum. In that case you might be safer if you convert one of your sources before ingesting, I'd still do it by slowing down / speeding up, but create that one intermediate generation of files ready for editing.

There are 3 camera frequencies on the GH4. 24hz, 50hz, and 59.94.

DCI Cinema 4k (4096 x 2160) is only found in 24hz. It is a tiny bit wider than UHD 3840 x 2160 (16:9)

Our televisions are 16:9, so UHD 3840 x 2160 is a better match for the 16:9 GH3 image.

You want the following settings:

System Frequency: 59.94

Camera resolution: UHD 3840 x 2160, 23.976 (23.98)

Photo Style: Natural for both cameras

You can still crop in for close-ups, but you won't have any issues with syncing.