The part file format document available here has the layouts
The difference between a through hole and a SMD part is that that SMD part only has the copper1 layer in pcb view where a through hole part has copper0 as a child group of copper1 and the copper appears on both sides of the board. An older format that had separate copper0 and copper1 layers (but for through hole the pads had to appear on both copper layers) is still supported and is sometimes useful for doing odd things. This tutorial series may help as well, as it describes how I make parts by editing the files themselves.
Part creation howto part 1 breadboard and pcb
As well you may want to change to the parts-submit forum category as posts here in About the parts submit category are not show as new posts in the forum (I expect there is something special about this particular topic) so most people won’t see the posts. I only came across it because the tool bar said there were unread posts even when there didn’t appear to be any. Clicking on it took me here.
Peter