Voyagers!, and Time Tunnel, and Quantum Leap. While Sapphire & Steel don't actually travel in time (at least, not on purpose), they do deal with an Enemy that does. And if the DWAITAS system is good enough for Cubicle 7 to adapt it to Primeval, it should work for S&S. Well, let's give it a try.
-Your characters are all based on "elements" that have taken human form and been assigned to repair time breaches before an unnamed Enemy (see below) gains a foothold in our reality. These aren't necessarily elements in the strictest chemical definition, but can be alloys (like Steel) or precious stones (like Sapphire). Transuranic elements (those beyond uranium on the atomic table) can not be assigned to planets where there is life, so do not make playable characters. See "Your Characters Have Been Assigned" for how to create and play an "element".
-Adventure scenarios normally start with a briefing that assigned the PCs to the location of a time breach. Such breaches are usually caused by the Enemy using a weak point in space-time, usually some anachronism - an antique, an old tune, or even someone who's time traveled to the present from the future.
-The Enemy is a catch-all term that may refer to a number of entities from outside time. These existed before time formed, or exist after the universe has ended, and from that vantage, try to enter history itself where their powers would lay waste to reality. They will often use "manifestations" of people who have died, either the echoes of these souls recorded in the fabric of space-time, or sometimes even the images of people they have taken to their realm. For that reason, a lot of S&S adventures feel like ghost stories. Cultivate that atmosphere as much as you can.
-In terms of that atmosphere, it is also in keeping with the style of the show to withhold explanations. Events aren't actually magical, but the lack of scientific justification is meant to enhance the suspense. Things humanity isn't meant to know, and all that.
-Though Sapphire & Steel's televised adventures all took place in the present day, time elements are so long-lived, they've been around forever. In fact, they've mentioned being aboard the Marie Celeste on its doomed voyage. So there's really nothing stopping an enterprising GM from designing adventure scenarios in different times, all across the PCs' personal timelines.
Your Characters Have Been Assigned
-There are two kinds of elements: Operators act as first responders, lead investigators and field leaders; they have a wide range of abilities. Specialists act as back-up, provide technical aid and have more specialized powers. Either way, they all have the following Special Trait:
Time Element is a Special Good Trait that reduces a character's Story Points by 4. It includes the following Traits: Alien, Eccentric, Feel the Turn of the Universe, Immortal (long-lived), Obligation (Major), Psychic Training, Quick Change (the ability to change one's clothes to suit a setting), and Telepathy. Time Element have other powers as well, unique to each one, though they may call on another element's power by expending 1 Story Point more than that ability would normally cost (see below).
-Each character's name is truly representative of that element's characteristics, and this should be reflected in both the Eccentric Trait (Steel is cold and hard; Sapphire is beautiful and fascinating; Silver is a flashy dandy; etc.) and in the powers one selects (Steel is strong and has a freezing touch; Sapphire can hypnotize; Lead is insulated against energy; etc.), though Operators should feel free to pick useful powers that don't have an obvious link to their element. These powers are all considered Special Good Traits and may be adapted from Alien Traits already in the game, or crafted specially for the element (such as Sapphire's Take Back Time). Powers take a lot out of a character, which is why they are used only sparingly. Each time a PC uses a Special Trait (except those included in the Time Element Trait), he or she must spend Story Points. The GM will decide how many depending on the use, though 0 to 3 is standard, usually 1 or 2.
-Taking our cue from Big Finish's S&S audio range, an element that is killed in the line of duty would be reincarnated into another version of that element. In other words, use the regeneration rules to recreate your lost character!
Here are the sheets I made for the two stars. First is Sapphire: