The way I see it, you have two options.
1. if you use manually loading in ida, you can set the dll-base on loading.
you will find the original dll-base with depends.exe or in the pe-header with a hex editor.
2. try some of those pe-rebuilders.
3. open the dll in a hex editor, and manually go through the peheader and find the correct values. then manually correct the file.