there's a parameter in magic data named "helps decide if a tyre set needs changing?", maybe you can play with it, to force CCcars to pit even with full fuel loads, but I'm only guessing: never experimented with it.
As for the CCcars having troubles with very poor performances, I think that by fine tuning physic file, performances, wing angles and gear ratios you should obtain acceptable results. I experimented some months ago a 50 laps race, no pitting, with my Hockenheim 70 track, and I had no problems; but to tell the truth I was using 2001 performances and physics, giving obviously more handiness than the ones to be used if you want to simulate an 80 season.
As for the crahes, how well the CC cars performs during the race depends on the CCline and car coaching settings too: you will notice that in some custom tracks having poorer CClines, the CCcars will crash more often than in other ones. As last measure to avoid it you can also modify the fuel weight in magic data, but be carefull with this parameter, because little changes give very different results.
Obviously you can only obtain a compromise, but I think it is just what F1 teams were doing at that times.