it is a beautiful quilt top! What a treasure!
A lady in my local guild told me that when I wash old quilts, to place them in the bathtub lined with a good strong sheet. that way when you lift it out, heavy with water, the delicate quilt won't be stretched or pulled in any way. She also advised that the wash be a simple soak with delicate wash detergent.
I hope you post pics of the finished quilt!
Blessings