rdnoel86 brought up a good point to remember: Those IMSA heads were done for an N/A application. Way back then, you couldn't run a turbo in IMSA(I don't know the rules now). They were pushing for 200-250+ hp with a Holley 500 cfm 2 barrel, and pushing 8000 rpm. In the middle of all of this development work, IMSA changed the rules, and the 2.2 became non-competitive, so Chrysler, Koffel, and the rest of them dropped the program. I'm not sure where the ITB setup came into play. Maybe it was a development deal, before the rules changed? I know all the pictures I've seen of the IMSA cars in race trim had Holley's on them.
I know there were guys out there pushing close to 300 hp N/A with these motors and radical heads. But that is close to the limit(IMHO).
I don't doubt what Shadow is saying, a propperly developed 8V turbo motor could produce close to 1000 hp, if money were no object...
But we're all T-M guys, and money is an object...