Audio does not have a frame rate. It has samples. Timecode is calculated as an offset from midnight (0 samples). When you import 44.1 it will become 48kHz, but duration will remain the same.
What is important for sync is what the frame rate was on the video when recording audio (44.1/48kHz) as that is what is in sync. For example, I can have one camera recording 24, another 25, and another 29.97 while recording audio at 44.1/48kHz. If I import each video into its own matching project and import the 44.1/48kHz file, they will all be in sync.
So your first step it to create a 23.976 project, import video and audio (44.1 converted to 48kHz). Sync.
Open bin with .sync clips in your 25fps project. MC will add a mix and match so you will see a repeat frame every ~24 frames. I have not tried this on .sync (subclips) ,but you might be able to change the play rate of both VA in source settings playback tab. Change it to :project.”
If not, then you need to make new source master clips. I would reccommend exporting OP1a with a finishing quality codec (DNxHD 120 or higher). Then link to that in your 25fps project and change playback rate to project rate.
Michael
Michael