Some thoughts ..

1.) the precursor to the csh is the newshell in {1}BSD.  It's Joy's hack to the Thompson shell and you might find it more usable.

2.) PWB 1.0 is based on a V6 kernel and has the Mashey Shell, which is in C and predates Bourne's  It might also be easier for you to use.

3.) srb wrote his shell during the transition between V6, TS and V7.   At least one version ran on the V6++ system we had at CMU, but of course as pointed out, it is written in Bourne-Gol. And I'm pretty sure his CPP definitions will need at least a gen2 /lib/cpp implementation***  However, Steve was also doing it at the time when the compiler was being updated.  FWIW: We also had the 'Typesetter C' running on our V6 system in those days.  So my >>guess<< is that v6 + Typesetter C - will compile the V7 shell.

Clem

*** Rob or Steve Johnson - maybe remembers when cpp first appeared.  I don't remember if it was part of V5 or not - those bits have faded from my brain.  What I do remember is there were a couple of different cpp's early on.  The first one was pretty crude by today's standards, albeit it was a cool idea and it was the one thing I really liked about C over BLISS early on [BLISS had Macros, which was cool aalso, but cpp could do things Bliss could not].