"C"-code

"C"-code usually needs no extra conversion tool, as long as you stick to naming conventions for file and subroutine names. Machine dependencies can be handled using the conditional compilation facilities of the preprocessor:

#if   defined(MVS) || defined(mvs)
... MVS code
#elif defined(VAX)
... VAX code
#elif defined(ultrix)
... ultrix code
#elif defined(_AIX)
... AIX code
#elif defined(OSK)
... OS-9 code
#else
... you loose.
#endif

Porting "C"-code means simply copying the source files to another computer.