Here it is!
The Big Finale!
(One codicil: may be NSFW due to racial stereotypes common to the era .)
Apparently very few people sent postcards because the Dover Boys have never been reprinted and never reappeared anywhere else.
And I do mean NEVER!
In 2011, Archie and Friends #137-138 and #150 featured a storyline involving almost all the "forgotten" characters from MLJ/Archie's long history from Suzie to Sam Hill to Super Duck crossing dimensions to Riverdale to encounter Archie and the gang...except the Dover Boys!
Sad, ain't it?