Well, you'd be porting away from graph then. Fine for a one off of course.
I was just thinking that porting the relevant parts of those old 2004 sources makes it all pascal (except for maintained libraries like SDL), and has the ability to be e.g. SDL less on Windows etc.
Anyway, no, I'm not aware of any headers. But there is a sdlgraph part of the FPC distribution, which might already have done this.