I use my 301 for FMQ all the time. I like the extra visibility of the slant needle. I bought my foot online from aprils1930sshoppe, which is now the Featherweight shop. I just looked and she still advertises 301 accessories, but I didn't see my foot with the large plastic part. There is another site with parts for vintage Singers, but right now the name escapes me. You can ask in the vintage machine forum. I want to try a foot with a open metal circle just to see if I'd like it better.
At this time, the slant needles do not do ruler work. Westalee told me that the foot would be available in November and they'd contact me. I haven't heard from them and couldn't find it on their site.