Joshua, I believe Maria typed "E C" to mean "Egyptian Cotton".
You are certainly correct about the differences between the old machines and new. I wouldn't want to part with either, but if push comes to shove the ones to bank on are the oldies with lots of metal.
If you haven't checked Etsy for the cams, that's randomly a source for vintage machine accessories. I found a number of Bernina cams there. I will keep an eye out for the cams. Which letters are you missing?
If you're serious about monogramming, an embroidery machine would be much more rewarding, IMO. Even a lower-end Brother embroidery machine will make a much more beautiful monogram than any sewing machine, and in versatile sizes. It will also do other fancy embroidery, of course, and you may find yourself taking on a whole new hobby, as I did about 2 years ago.
Of course, if you have the patience and skill you can learn to do freehand satin stitch embroidery and monogramming with a zig-zag machine. In 1966 I watched a sewing machine salesman demonstrating this technique on a brand new White zigzag. He made it look extremely easy, but then I tried it.
Here's a video by Clare Rowley that shows the basics. She makes a ridiculous statement that a 3 yr-old could have fun with this - no, no, no and no - sorry, that's just nuts! The video is extremely slow getting started and she's pushing her products, but I didn't find a better demonstration or one on a vintage machine. Interestingly, she mentions that "we used to" be able to adjust the zigzag width while sewing. Those of us with old zigzags still have that option. With her skills, you could do it on a straight stitcher. You could slide this to the halfway point if you just want to watch the embroidery part and miss the cute doggie and other asides.
https://www.youtube.com/watch?v=FDzwY5nJZp4