Most of the code is written in an old-fashioned style, but rather than redo that, it's more productive to convert to D, and then into a modern style.
I'm not sure what exactly you have in mind for "modern style", but I found the code as it is to be quite readable and a breath of fresh air from a lot of other code I've heard referred to as "modern" (which seems to mostly mean laboriously long identifiers, excessive amounts of abstraction, and CamelCaseScreamingAtYouEverywhere.)