Rewashing is a good idea followed by a clearing agent and again rewashing. Selenium toning is also a good idea to preserve whats there but they must be toned to completion to be of any help, which will increase the contrast, but help some in preservation. A SISTAN bath after final wash will also aide in this.
Be careful of the thinner negatives as they can have a tendency to curl severly while drying. ( I've seem some actualy curl up on themselves) It would be a good idea to test one before you procede to avoid the panic of a cabnet full of curling negatives. Another issue is the proper storage of these negatives afterwards to help avoid further problems, especially after going to all this trouble.