Actually, this is a download model - so you essentially buy a pdf that you can then print out pretty much any size you want (well, provided your printer can handle it of course). So no need for scanning, and downsizing is just a matter of adjusting the print size.
One method I have followed in the past when 'transfering' paper kits to more sturdy media is glueing the structural pieces that you invariably get (that's those that go inside and won't be seen once it's finished) onto heavy cardstock or plastic sheet. With fairly simple shapes that works well. The problem here of course is it's not an quite so simple shape...