This: http://distrowatch.com/table.php?distribution=tinycore seems have installed Xorg.---There is a super minimalist version called Microcore with the total bare minimum system. Only 3 files total. Gather all the libraries you will need in a folder and ISO it together for a custom distro.
BTW, what window managers written in FPC ? Are there any links ?
Are you talking about a window manager like fgGUI?