Dennis Ritchie has placed some of the earliest surviving C compilers up on his web page at http://cm.bell-labs.com/who/dmr. The web page primevalC.html describes the history and features of both compilers. The two -bits files are the original V2 tap archives. There are matching .tar.gz files with file timestamps preserved. If you want to use these compilers, then the binaries and a suitable emulator are available via anonymous ftp at minnie.cs.adfa.edu.au in the directory pub/PDP-11/Sims/Apout. The prestructc compiler can be compiled using the above binaries with a few source code changes. The changed source is in fixed_prestructc.tar.gz, which also includes a context diff file showing the changes made to it.