I just found this online, but it's an interesting experiment.
What-if in 1979-80 Grosset & Dunlap had completely lost the rights to #'s 1-58 or the judge had said that G&D could continue publishing those numbers in hardcover, but the Stratemeyer Syndicate and Simon & Schuster could publish them in paperback, what would the look like in the Wanderer Arches?
Someone's done that and the covers are interesting. The House On The Cliff & Mystery of The Spiral Bridge really stand out!
http://www.hardyboysonline.net/content.php?page=series-canon-hypcovers
Wow! That's really cool! I haven't looked at that site in quite a while. Thanks for posting the link. I think the cover style works better for some than others using that artwork. I think Simon & Schuster would have had to create its own cover art. I like how a few in particular came out. I agree with the two you mentioned; I also like The Jungle Pyramid, Danger on Vampire Trail and The Crisscross Shadow. 8) :)
Very cool artwork!