Are there modifications to the hit point rules? I mean, Call of Cthulhu investigators are pretty squishy, and I probably wouldnt want superheroes that died that quickly...

Not really. However, the Super Powers rules let you buy a huge CON with Super Characteristic and there are four powers that effectively block or reduce damage. It seemed to work okay in Superworld back in the day. The BRP system would not be my choice for a pure supers game, however -- at least not a four-color one.