Thanks to Jon's tips, I broadened my search a bit and think I found a shuttle, it fits anyway, and looks locked in place. I've never used a vibrating shuttle machine and once I had it threaded and went to test, the top stitch looked OK but there were tons of loops of thread on the bottom, all about 3/8" long.
I tried searching the forum for this problem but my search terms were too common so the results were more generalized.
Can anyone point me to a thread which might address this problem?
Thanks!