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.