There's definitely not much out there on them. What little bit I've found as far as diagrams go, are here (which you've probably seen already)
http://excalibur26.com
They did have a couple different layouts over the years, notably with or without the galley. Manuals would be almost non-existent at this point, I'm sure, if they even had anything originally. With such a small run overall, it's not too surprising.
Is there anything in particular you're looking out for? I can try to help in whatever way I can.