GPLv2 actually requires more here than GPLv3. Although GPLv3 only requires the work as a whole to carry a prominent notice that you modified it, GPLv2 requires it of individual modified files:
a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.Distributing the original source plus the patches would meet this requirement, at least in spirit although perhaps one could argue that for the modified files to carry prominent notices you'd actually have to insert obnoxious comments into the files themselves, rather than providing that information "out-of-band" in the patch set.
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