Hi Diana,
What a wonderful find. I would use the gentle quilt cleaner found at your LQS. I would then soak the top, rinse, squeeze out, do not wring, the squeeze in a towel, then air dry.
The other option is to take apart, and hand wash each block and lay on towels to dry. Then iron before putting into the new top setting you desire. They will look great. Do you have any ideas for your fabrics and layout?
Good luck with your project and please keep us updated with pictures if possible.
Pam M