Have you checked out Godlike (which seems to be pretty popular right now) or WEG's d6 Heroic system (as contained in their DCU rpg?) It seems like the hardest part is coming up with price lists, etc, and placing limits on powers, as in comics heroes typically weren't as out of control in the golden age (20-30 years after the time you're talking about) as they are today (even superman was weaker).
To be honest, Hackmaster is probably your worst choice here. You'd have to create coimpletely new classes, which includes entire new sets of rules. Their current system is very unlikely to work for a fast-paced action theme (yes, there's a lot of combat, but like AD&D 1st ed, it's slow).
I'm not familiar with Space 1889 or Hero, but GURPS has a decent enough supers supplement already in place. I'm not using it, and I could bring it out and loan it to you on an extended basis if you wish (when I come in a week or so). D20 would take more work than GURPS, but might be rewarding enough to make it work, just for the less tedious-ness in everything. Though it seems to me that Feng Shui would actually take less adaptation than d20 would.