70 Stage 1 Head Damage - OK or scrap?

I had no idea why you were concerned with the #5 piston, but there was a bunch of debris there. The stem of the valve was in the intake manifold. Obviously a powerful convection created. Pic of #5 attached.

 

#5 shares the intake runner with #8 so is the first to share shrapnel, next up #'s 2 & 3 off the same side of the plenum. If you plan on using that intake when you think you have it cleaned out, clean it again . Any residual debris will ruin your efforts in no time.