Hi,
if you are missing a runtime library like msvcp71.dll, you can download tha amd64 version directly from Microsoft:
However, if I remember correctly, the amd64 version of the WRK tools, should require the xxx80.dll version of the runtime libraries of Visual C++ 2005. All of those should be contained in the respective tools directory already.
Best,
http://www.dcl.hpi.uni-potsdam.de/research/WRK