Hi, dududas! 
I actually had made requests about this a couple of times before. Here was the second request I made:
Dan kindly added more decimal points to the speed control in the Properties tab after each time I requested it. So it went from just 2 decimal points to now 6. After experimenting A LOT, I came to the speed change of 0.95902 to convert PAL to NTSC speed. Please try it and see how it comes out for you.
Based on audio, the conversion comes out right. The only issue is that the frame rate for video will vary by a frame or two every now and then. I’ve done comparisons with video that were sold in PAL and an identical one sold in NTSC. Sometimes the frames will match up but every now and then they will be off by one or two in the converted video then match up later but then down the line be off by a frame or two again. I don’t know if this is normal when converting a 25fps source to slow down to an NTSC frame rate such as 29fps or 23fps. Or maybe the issue could be that more decimal points are needed to get the frames to match up perfectly. However, Dan in the thread above said there was a bug with the spinner control. That thread is a year old so I don’t know if the issue has been fixed or if it still exists. @shotcut, any updates on that?
I should note that the issue with the video is not noticeable at all unless you are actually comparing the frames between a video that you converted with one that was commercially converted to PAL. Also, for me this is all in SD because they the PAL videos I have are from DVDs so I didn’t convert them to NTSC 23.976 but instead aiming for NTSC 29.97.
@Austin, would you happen to have any knowledge in this area?