Assuming you are talking about buying new heads and not scrounging a pair of Stage VIs, which are no longer made.....

http://www.manciniracing.com/bigblalcocyh.html

MP heads which are Edelbrocks with straight plugs, $889.95 each

Edelbrock heads, which have angled plugs otherwise same as above, 809.95 each

Either head will get you 600hp pretty much straight out of the box.

R.