I’m not sure how the PAL to NTSC conversion was done because it was handled by a facility outside the country. I will attempt to find out.
But, just to be clear, the original footage was shot in PAL. The new soundtrack was mixed to the PAL picture. Shouldn’t that audio be in sync?
(The NTSC video conversion was done “after” the new audio mix although, due to delivery deadlines, I did the post edit of the NTSC first, without any audio issues.)