Hi Spajo , head stock "junk" ? Unusable ? Maybe , maybe not . Obviously the two bores must be inline , depending on how big the crack was and how it was held in place when brazed maybe it's ok . If I was going to save the little 6 inch I would disassemble the spindle , check it over for any galling , how badly is it worn ? Then check the broken bore , if it's round (not brazed back crooked) then I would get new bushings and reassemble . A note on the bushings , they are not supposed to be split and they don't need a oil hole . I think your spindle is overly worn as is mine . I split (one side) my bushing and drilled a oil hole . This allows me to adjust the tightness so that the spindle runs good .
Good luck keep us posted , Mark .