The Hardy Boys Ultra Thriller Series

Tom Swift joined forces with the Hardy Boys for two books in this short-lived series published by Simon & Schuster under its Archway imprint.
Produced by Byron Preiss Visual Publications, Inc.
Cover Art: Romas Kukalis (1), Michael Herring (2)
Format: Neither volume contains internal illustrations.
The first book has a medium blue spine & back and yellow page tops
The second has a very dark blue (almost black) spine & back and plain page tops.
No hardcover editions were published although library hardcover rebindings may exist.
Despite the use of the Franklin W. Dixon pseudonym and some Casefile-like elements, the stories are more closely related to the then current Tom Swift IV series.

For Sale items are available from Amazon.com.

Hardy Boys - Tom Swift Ultra Thriller #1 Hardy Boys - Tom Swift Ultra Thriller #2 1: Time Bomb - August 1992 -For Sale
   A dream that has long fired the human imagination has become a reality: time travel. But as Tom Swift and the Hardy boys are about to discover, the dream can become a nightmare in the blink of an eye. An attack force of techno-thugs, under the command of the evil genius the Black Dragon, have seized control of a top-secret time-warp trigger.
Frank and Joe and Tom leap into battle--shock troops in a war that stretches across the aeons to the edge of time. But whether chasing asteroids or dodging dinosaurs, they haven't a moment to lose. They must stop the Dragon before he carries out his final threat: turning the time machine into the ultimate doomsday device!

2: The Alien Factor - June 1993 - For Sale
   Tom Swift has caught a falling star-- a visitor from outer space who is as beautiful as she is strange. But his secret encounter has set off alarms at the highest levels of government. A top-secret intelligence agency believes he's involved in an espionage and smuggling ring. To check Tom out, the Network sends two of its top operatives: Frank and Joe Hardy.
But when the alien is kidnapped by a sinister industrialist, Frank and Joe and Tom realize they have to work together. They're dealing with a conspiracy that stretches from the farthest reaches of space into the deepest recesses of their own government. The fate of the country and the planet could rest on uncovering the shocking truth about the girl from another world!