There is a D6 superhero game on the web, though. It's the D6 Marvel Superheroes game. The copy I originally got is by T. Catt. But as far as I can tell the rules are currently only available on the Arcane•Marks game page (at the bottom) in a version by Talon Dunning. I guess it's the same cat.
This is the old cover
Anyway, the game is not based on the Legend rules, but on a slightly modified version of D6 Adventure. The biggest change is that the D6A attributes (which were the same as the Legend ones, BTW) are replaced by the FASERIP attributes from TSR's old Marvel Super Heroes Roleplaying Game. Fate Points work the same, but are now called Karma points like in the old MSH game. There are also new rules for Popularity which are somewhat like the Reputation rules in Mekton Z. The most surprising part is that there isn't a new system for handling super power. Instead the game just uses the Special Abilities form the D6A rules. Players are encouraged to add new abilities, but the stock list works surprisingly well for most super heroes. Two new powers are included, Wall-Crawling (3) and Power Cosmic (15). For characters like Dr. Strange or Jean Grey who have magical or psionic powers you just use the Magic and Psionic rules from D6A. There are two sample characters included, Spider-Man and Wolverine, which gives you an example of how the rules work.
It's a pretty clever use of the stock D6 rules to handle a super hero setting. Using the Legend scale, I'd say it would work good for Power Level 1-2 games. But higher level games featuring powerhouse characters like Thor or Hulk would be harder to run. For example, Spider-Man has a Lifting skill of 10D+2 which means he can lift 1,400 kg. That's impressive, but it's nowhere near the 10 tons he's should be able to lift. Another problem is that the cost of some of the Special Abilities in D6A are a little off. For example, Elasticity, which gives you the powers of Mr. Fantastic, costs only one point per rank. Meanwhile, Ventriloquism, a far less useful ability which just lets you throw your voice, cost three points per rank. So in my opinion the D6A rules might need a little more tweaking to work well for superhero gaming.
Which is not to criticize the author of D6 Marvel Superheroes, who did a great job. The game is an excellent example of how to take rules in an unexpected and fun direction. If you want to run a superhero game using a free set of rules these would be a great choice.