YES, you can have assemblies with same name in GAC but their versions needs to be different.which version client want to use just right in new version...
GAC is just a Folder that contains .dll that have strong name.We can say that GAC is a very special folder, and it is not possible two place two files with the same name into a Windows folder,But GAC differentiates by version number as well, so it is possible for MyApplicaton.dll and MyApplication.dll to co-exist in GAC if the first one is version 1.0.0.0 and the second one is 1.1.0.0.