4.0 V6 Head Removal

I've got a '93 Explorer with a 4.0 V6 (pushrod) that I'm trying to remove the left head from and discovered that I need a pretty big Torx to get the interior head bolts off. Does anyone know what size it might be and where I might get one? My local Ford dealers have been less thatn helpful, refusing to sell me one.

Thanks in advance,
Steve near Chicago