Take the cover off the front and the radio off the back. You can look through the port to gauge the target zone. You can proof in google earth when planning the site.
Twist port alignment scope/tool.
The tool could be your cell phone camera in a twist port that holds the phones camera in the right place (or a GoPro). And an app for PC or other device that allows you to look at the target coverage area in google earth to make a target picture. Then when you are on the tower with the twist port alignment tool it will show you the google earth picture as an overlay or simple cross hair or ring. The app could have a selection to choose the horn you are using.
Or maybe a simple tube with an eyepiece, it could slide in and out to the correct field of view to match the horn. I think a clip on spotting scope would be easier to manage on the tower. Maybe clipping to the back/smallest ring where the set screws are. Or even something that clips to the front.
Just my thoughts, Sorry for rambling.