You don't... you get one already made. It IS possible to do one yourself with the rigth techniques and data. But even with any perchant for.... mmmmm.... creativity LOL..... I'd just buy one.
this was helpful. The multitude of shallow holes in mine were a source of much confusion.
update: the SCAT stroker kit and a Comp XE275HL K kit are on the way. I was a little concerned about the 106* lobe separation on the Howard, but the matching valve train recommendations listed in the Comp Cam Catalog tipped me the rest of the way.