It took me 3 months to make my first totally new part, simply because there were no instructions and no help. I had to reverse engineer it by looking at other parts and use trial and error to work it out. I taught other guys what I knew, and they worked out other bits that I missed and taught other guys, and now we kind-of know what we are doing.
In the XML structure of the PCB view - I use the XML Editor in Inkscape - you just have to add a node above copper and call it silkscreen. And in that you add a rectangle representing the outline of the board - the rectangle has to be accurately positioned in relation to the contacts because this is a simple engineering drawing fit for production.
Then just add the 4 accurately positioned mounting holes/circles into copper.
I'm not a BB expert so I don't know why the contacts don't mate with the board - probably missing some XML nodes -, so I would have to reverse engineer it from other parts.