95 t-bird 4.6 head swap

[jworm420]

I have ben wanting to do a head swap for a long time on my bird... I wanted to get a set of PI heads and Intake to get some more power out of my bird. I have herd some people say that you can not put PI heads on a Gen 1 4.6L block. Does anybody know why ?
As far as i can tell or figure the only reason that you would not be able to make the swap is if the pistions are different in my gen 1 block then tey are in the 99+ 4.6's with the pi heads, maybe the duration of the the vavles staying open is too long and the pistons would slap the cams at higher RPM's... if any one has any info on this please let me know, or if you are saling or know some one who has a set of pi heads for sale please let me know.