The Excalibur is one of those planes where the fuselage is built upside down on the top block.  It’s a nifty construction method that Joe Bridi employed extensively with his planes (although this is not a Bridi design), and it’s also seen in a lot of other pattern planes including the New Era.

The Excalibur looks to me like a miniature version of the New Era, which was published around the same time.  It has a thicker airfoil, and a relatively longer tail moment.  The plan shows an OS 10.