MEMORY:

I think the only way the Hardys could have ever made it into television back then was to be repackaged as a bubblegum band. It was Filmation's answer to Scooby-Doo, who debuted the same season (1969), mixing in the bubblegum pop of the Archies, who'd debuted a year earlier. Sadly, no one's thought of trying a new Hardys cartoon w/o the rock & roll gimmick. The books have changed with the times, so kids may be ready for a new Hardy Boys toon.

Archies in Toys
The Archies in Music
Bubblegum in Food