I looked up the Westalee foot, and I think it should work fine. A 99 threads from left to right, and it's not an isssue for tis foot. The only thing I know is that jumping feet are a fuzz to find for a 99. It has a slightly different angle to the neelde and presser bar, some jumping feet end up dragging the entire presser bar half way up during stitching. I can't see any trouble with a low shank Westalee foot
from pictures. I know some have managed to darn and free motion well on a 99 and 66, it's not a favorite for the job like a 15. The horizontal bobbin case might be a bit more fuzzy when it comes to getting tension right, or it's just me because I hardly do any free motion. On this forum there is woman who has removed the feed dogs on a 66 and set it up exclusively for quilting and free motion. A 66 is the larger version of the 99. I hope get the spool pin straight again, it can be replaced. They are slightly tapered at the tend and go in with a light tap of a mallet or hammer with wood piece in between to prevent dent marks.