Although we don't have the actual toy, Bill Bulloch found the origin of the Spacex Salvage Craft. It is based on salvage spaceship GK-10, which briefly appears at the beginning and end of a Fireball XL5 story by Eric Eden, published in TV21 #87-89 in October-November 1966
In the story, GK-10 is on its way to a planet serving as a spaceship graveyard, when its crew gets notified that a dangerous live nuclear reactor has been dumped on the planet and that somebody's just landed there who can't be contacted. XL5 is closer by so goes in to avoid potential disaster. But on the planet a salvage merchant has already found what he thinks is an empty reactor housing, and is towing it to his ship when things go badly wrong. Steve Zodiac manages to save the merchant, but the merchant's ship is lost in volcanic action after the reactor has exploded.
Remembering the unwanted ship GK-10 was towing to the planet, XL5 makes rendezvous with the salvage craft so the rescued merchant can take over the towed ship to replace the one he lost on the planet.
