Thanks to Geobra shutting down Playmofan's Plans site, Heather and I have revived the idea of a pictorial guide which will not infringe on any copyrights.
I've started with 3667, and will in the next week or so be adding 3030, 3666, 3888, and combining 3888 with the 3666 and 3667 castles. The Rock Castle and Empire Castle will hopefully follow in due course.
I'm creating these primarily for Playmoboard, where we get a lot of people asking for plans to these older castle sets, in the hopes that this helps them, and reproducing them here in case they are useful.
The part numbers are linked to Heather's Playmodb, and the pictures are hosted on my Photobucket account. Feel free to use the pictures for anything you like.