That is fabulous!
I have learned (through the guild) that any time you add to a vintage piece, the piece is then dated from the date of the newest work done. If you are trying to maintain it's vintage value, then it might not be best to complete it.
However, if you want to finish it so that you can use it, you may want to stalilize it first before quilting or tying it.
I did a search, and came up with lots of advice to finish a vintage quilt top:
https://duckduckgo.com/?q=finishing+...=v177-1&ia=web