I am trying to find out what headjoint I have on an older Yamaha 581 purchased around 1993 the only marking on the back is a * and it was supposely a custom headjoint.

98% chance that it is a handmade CY headjoint. It's a fine headjoint that's suited well towards solo and jazz work more than orchestral, IMO.

From the info i have been able to find out if it is a handmade head joint it should have CY and silver stamped just below the crown on the back and if it's machine cut it will not be stamped.

I have a yamaha 511 sterling head joint, body and foot closed hole made around the same time and its stamped and easily read. The old 500 series is now the current 600 series flutes.

I cant comment on what there like as the CY head joint i have has been customised

Ah - then it's probably not a Yamaha headjoint but someone else's that's been sized to fit the flute.