I would have a look at the AP-387 for such a situation as standalone point-to-point. This AP has a 60GHz high throughput radio with 5GHz backup (or actually load-balancing).
If you prefer to have it integrated with your controller, you can use a pair of the AP-387 as well in mesh, or an AP367/AP377 for standard 2.4/5GHz Wifi mesh with the existing AP-304.
It is not required to have the same AP or antenna on both sides, but please seek advice from your Aruba partner to evaluate the available options.
Using indoor APs with external outdoor antennas is typically not recommended if an outdoor AP with built-in antenna can do the job. External antennas are harder to install and cabling of external antennas is in general less reliable compared to the antenna built-in the AP.