Just as the scenarios for Treasure Hunter Adventures can be modified for use in the time period for Raiders of the Lost Ark, elements from the supplements can be used to create adventures and campaigns. Here are a few of the possibilities.
Treasure Hunter Adventures
As mentioned previously, the character Archetypes provide ready stats for heroes as well as the NPCs whom they encounter.
When it comes to the Level of Magic for an adventure or a campaign, as noted, Low Magic seems to be a good fit. Relics are rare but can be quite powerful—which leads to individuals and organizations wanting to gain control of them.
Jennifer Flannery could be an employer, a rival, or even a romantic interest for the heroes.
The search for the Silver Madonna would be a good introduction to a bigger adventure, just as Indy's pursuit of the golden idol opens up Raiders of the Lost Ark. Perhaps the GM could use this to introduce an enemy, like Belloq, who steals that prize.
THA2: Prizes, Puzzles and Perils
All of the relics detailed in this supplement could, of course, serve as the prize for an adventure. Indeed, the Clavicula Salmonis is a good fit for a relic that the Nazis are seeking in order to tip the balance of World War II in their favor.
The various puzzles, traps and locations could also be added to adventures.
Finally, the organizations can play many different roles in a campaign. The Office of Special Services could try to recruit the heroes, while the Vatican Secret Archives might be a rival. The Rosicrucian Order could also be rivals, albeit with less altruistic motivations; the Thule Society would provide a veneer of cover for Nazi sympathizers.
THA3: Underwater Salvage
At first glance, some of the technology introduced in this supplement might seem too advanced for the time period in Raiders of the Lost Ark. It was just after World War II, however, that Jacques Cousteau began renting the Calypso to use for underwater salvage.
Here again, the locations of lost ships and sunken cities, along with deck plans for vessels, and new hazards, hindrance and edges, provide fodder for adventures.
THA4: Mercenaries & Magic
The Condottieri Mercenary Company provides an excellent group of rivals for villains in its own right, but the character stats and compound map could also be pressed into service as a Nazi expedition and their base of operations.
Ephraim Grey, along with his sons Ezekiel and Ezra, could serve well in the role of scholarly advisors for heroes who need some help with research or translation—much as the Imam does for Indy, reading the inscription on the medallion in Raiders.
More puzzles and prizes are useful here, too.
THA5: Saints & Sinners
While all of the prizes detailed in this supplement are potentially useful, the Golem in particular seems to match with the sense of religious mystery present in the Indiana Jones movies.
Any one of the holy places detailed in the atlas could serve as the backdrop for a cinematically styled adventure.
The various criminals who make up the Syndicate can be excellent rivals for the heroes, especially if pitted against them and other villains.