Grosset & Dunlap/Chatterton Peck hybrid

This is truly about the rarest of the rare.  Two are known to exist.  It could be considered the 1st Grosset & Dunlap printing, but only because the cover is stamped Grosset & Dunlap on the bottom of the spine.  Before G&D began publishing the series in the first format, they purchased some unbound interiors from Chatterton Peck, who had printed the series before G&D.  They printed new covers in the original Chatterton Peck format, but with Grosset & Dunlap on the spine, and put them on the Chatterton Peck interiors.  So the cover is G&D and the interior is CP.