I was actually performing some additional ad-hoc tests while doing this. I am attaching the patch which extends the test for different target process (including 32 -> 64 and vice versa). To run that I copy 32 bit ntdll_test.exe as ntdll_test32.exe along 64 bit ntdll_test.exe (to be run), and ntdll_test64.exe to the 32 bit test directory.
A more meaningful case would be to test large address aware/unaware apps of the same bitness.