i ran a 400/499 race engine a few years back, the pistons were real short & the 7000 rpm made the short piston skirts wear real fast. About 3 freshen ups & those pistons were trash. I have a 400/512 motor in my street/strip car, Molnar rods & Crank, (not a fan of the junk Source or Scat brands), the pistons are lasting much longer, longer skirts seem to be the trick. With Stage 6 MW heads & a 272@0.050 roller cam & a 850 carb with 10.5 cr, this made 645 RWHP on a mobile chassis dyno. gets my full factory optioned 71 cuda running 10.5@125mph. Is this the kind of performance you were looking for?