Check this site. Blue-thunders $850 each, bare.
http://ford-y-block.com/sbf_head.htm
Hope that helps, Steve
P.S. Don't let the "in-line valvers" sway you in your quest for Mustang power. I'm using a set of C heads that flow 335cfm on the intake with a 372ci Windsor block and I love them. I'd sure like the reduced weight of some al. heads though; they'd take about 50-75 pounds off the beak of my Boss!