[racket] Book parts in scribble

I'm trying to achieve something like Latex's \part in scribble and not 
sure what the right approach is.

I want

I First part
1 First chapter
2 Second chapter
II Third part
3 Third chapter
4 Fourth chapter

Should the parts be sections that include-section each section for the 
chapters?  But then how do I get the Roman numbering of the parts, and 
how can I restore the chapter counter so that it doesn't reset to 1 
within each part?

Or should parts just be a kind of section that exists at the same level 
as chapters, but with some custom style?  But then, how do I get the 
separate counter for part numbers, and how do I render them with Roman 
numerals?

Thanks,
David