Size chart:
Legendary Helm, kiddy-sized (for most folks)
Molded helms, adult-sized
Pep helm, any size you want
Point is, there are lots of better alternatives out there.
Oh, and recasting is looked very very down on so not a good idea unless you just want one for yourself. Trutfully it would be cheaper to just gut a H3 Legendary helm than trying to recast it.