As I remember reading on the swap, there is a plug that must be installed on the back (facing the firewall) of the drivers side (left) head or oil spillage will ensue. Even thought the head castings can be swapped side-to-side, the plug must be installed on the left head. Remove it from the old nPI head and transfer it to the new one. Or......
This is covered in the "Great New PI headswap write up" at the top of this page. It states there that ANY plugs in the old nPI heads should be transfered to the PI's...... I'm really just thinkin' you just installed your PI heads opposite from where they were on the previous PI block and the plug you need is actually in the front of the head you installed on the pass. side. (right) I know.... you don't want to hear this.
Yea, it's tight back there! Don't forget the teflon tape on the threads!
GT