This discussion gives a hint of the basic differences between these two languages. There are many others that pose stylistic, but not fundamental, problems. Portions of the converted code simply do not look like good C code - it looks like converted Fortran. This converted code works well and does get the job done efficiently. Converting it to the C way of doing things has become a continuing part-time effort.
Some general observations follow.
The C code is slightly faster than the Fortran version. This is mostly the result of a general cleanup of the code's kernel rather than differences between the two languages. This is also contrary to rumors of loss in speed for scientific calculations in C. One striking difference is the fact that, on the average Unix box, the C development environment is better than the Fortran. This includes the many types of lint, source level debuggers, integrated development environments, and peer support, and reflects the fact that the OS itself is a C code. The feedback from the user community has been largely positive.