Oh, I wish I could be more help! Last time I sewed clothing was probably the mid 1990’s. I’ve only done an invisible zipper once. It was ok, but I’m not an expert at all. My mama, though, she could tell you everything you want to know. Alas, she’s in Heaven, so we can’t ask her. She was a talented seamstress. She designed her own clothing when she was a teenager, and even designed (and sewed) my wedding dress, which was just beautiful. Times like this I really wish I could call her on the phone and chat. She’d know exactly what to tell you. Good luck with your project!
Your Mom sounds just like my Mom. They are probably both in the same sewing room in Heaven :-) I have most of her patterns, she had quite the collection starting from the late 1930's.