So I've won the eBay auction (no other bidders on the lot), and sent payment. Now we wait for it to arrive. My hope is that if it's nearly as old as what I have, the color will be a fair enough match, and I could hold two or three strands together to at least finish the sleeves with near-enough matching yarn (this is Mary Maxim worsted weight pure wool, and I need Mary Maxim Northland wool). Of course, that might look just awful; maybe I should ply them together on my larger drop spindle. Wish I had a spinning wheel with a bulky bobbin right about now! Will have to play with it a bit and swatch and see what works better.
If the Cadena is a better match gauge-wise, and not too bright a color, I could just use it to finish the sweater and add in side panels to make it fit, and be done anguishing over it.
It's a special sweater to me in that my grandmother knit most of it. I can hold it to my face and smell her in it. We are almost two thousand miles apart, and Alzheimer's is taking her further and further away from us every day. It will have both our handwork in it together, and others might question the final product's appearance, but it will mean the world to me. :)