I've been doing a bit of research into how the various cylinder heads compare flow-wise, and came upon an exceptionally interesting thread on another forum. A fair bit of info in it, and not just on heads. I saved it (as a pdf)
for future reference and if anyone else is interested there is a copy of it at http://www.jmurray.id.au/holdenheads.pdf (http://www.jmurray.id.au/holdenheads.pdf)