Below is a picture of said ad:
I'm thinking the book "Drago" you asked about is the same as "Flyin' Fools", (see the same ad above) which never appeared in the public hands except as a reprinted book from Eclipse as "Bob Powell's Timeless Tales", March 1989 for the first time with the same cover except for the title name change.
A few others from said ad never made the grade either: Bruce Gentry (as a Harvey book), and Boy Heroes besides the other two mentioned above.
Would hope that answers your question and anyone else that see the other 3 books that never saw print at the time of the printing of the above ad.
Geo