I think these might have been one of those "Seems like a good idea at the time" efforts.
I was in the system for the great majority of the Inter's service period and never saw or heard of this kit.
I wonder how long the roof would have remained without stress cracks. I certainly would not have liked to be standing up there like the proverbial awaiting return serve from the people you are shooting at.
Would be a great novelty at a show to see a vehicle set up with all the gear.
Here appears to be the full Inter story (40 minutes, maybe the roof mount is in it - haven't watched it through yet)
https://www.youtube.com/watch?v=Roj2G5uNptA
PS Just watched it and this has the mount operation on it. Love the fake pommy accent which was compulsory for narrators until the mid-60's and the "Family Going to the Beach Holiday" music which also seemed compulsory for Australian docos of the period.
Lang