I am not familiar with the fitting you mention, however 'Hollaender Speed-Rail' makes many styles of fttings beside the ones commonly seen at the whitewater shops. Here is a link to a catalog....
Hollaender Aluminum Speed Rail Fittings
Would the #12 short barrel cross work for you?
Speed-Rail fittings are commonly used for industrial guard rails. Once I knew what I was looking for and could describe them using the manufactors name and number I was even able to get them at a local industrial supply house and avoid shipping cost.
The correct length set screw should be counter sunk just a bit, so I wouldn't worry about them in contact with the tubes.