Generation III Internal Engine - cam swap: remove heads or not?

I have heard that not removing the heads during this process can cause distortions in the block, and that GM recommends head removal when swapping cams. anyone else heard of this? I don't have a manual I can refer to. thanks in advance
<img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

i have never heard of this.

Go to www.torquecentral.com (http://www.torquecentral.com)

it has explicate instructions for a cam swap

I have done a few swaps and never removed the heads....

I didn't do it on mine, and no problems so far.

You do NOT have to removed the heads.