You may want to contact your local or state historical museum. They can put you in contact with a local textile conservator who could advise you of the right way to clean your quilt. When in doubt, go to the experts.
If you want to do it yourself, I would fill up the bathtub with warm water, add some Orvus (not sure of the spelling) and gently handwash in the tub. Gently squeeze out the extra water (NEVER wring or twist). Roll the quilt up in towels and gently squeeze out the water. Continue changing the towels until the quilt is almost dry and then it should be ok to hang it to dry.