I guess my first question would be...how is the quilt to be used?
Will the repairs significantly affect the value of the quilt?
To replace pieces...I would applique the reproduction fabric OVER the area. Sometimes cutting out the area will weaken the quilt more.
Here is an article concerning basic quilt repair and restoration
http://www.quilthistory.com/repair.htm
Perhaps others here have other ideas...
Good luck with your project!!
FW