Hello Tony
You should not mix the antenna typ within one radio module.
If you use just one antenna per radio you will lose most of the 802.11n advantages. I would not recommence it.
In the Extranet under the part AccessPoints you can find document providing a lot of information regarding antenna installation:
Extreme IdentiFi™ Wireless: External Antenna Site Preparation and Installation
If you are using omnidirectional rod antennas each they should orientate into a different direction per radio module.
If your APs are connected by fibre, maybe you can install the antennas without a lightning protector.
Kind regards