I'm looking into this also (put up a new thread last night). From my understanding the '96+ is 9.3, the '00+ motors are 9.74 and swapping the PI heads onto a pre-'99 motor should put you at about 10.5. I've read this in a few articles and wouldn't be suprised. The combustion chambers on the PI heads are much smaller than the stock heads, almost non-existent.
The other thing to consider is the difference in piston dish depth. These varied through the years and through the different applications.
Mine checked out to between 195 and 205 on each cylinder post headswap. I was close to sea level (South Carolina) at the time and if memory serves the formula yielded approximately 10.25:1 compression ratio.