where to start?
cut out the dent and see if you can get a sharper dent casting from someone.... cut out the back slots and put a decent mq-1 casting in...... get an aluminum rangefinder stalk from someone (BKBT maybe?) chop out the vinyl/plastic visor and get a t-visor from somewhere...correct the shape by either securing the visor or putting in a brace at the bottom of the helmet...
that should be decent enough to get it up to par...then just paint it up
hope that helps/made sense