IIRC, it's a 54"L x 1.5"H x1.5"W square aluminum bar. Securing the beacons' bases on the bar won't be hard, I'm sure, as self-tapping short screws were used (not entirely sure, need conformation on this).
Are you planning on putting mounting feet on the bottom as well? I know that if you want adjustable mounts, the original Visibars have a 6 to 7 in, machine-cut channel on each side in the center of the bottom, starting I believe 3/4 in away from the end of the bar so that you could adjust the feet more in or farther out to fit on the roof of a vehicle properly before tightening them down. How to do that yourself without taking the aluminum bar to a machine shop is a new one for me.
Here's Eric6913's CT-1 Visibar, showing the bottom profile of the aluminum bar:
I have a plain visibar, no endcaps, no mounts, that I could send you for shipping costs. The beacons mounted with 1/4- 20 bolts, 1/2 inch long, there are pressed in inserts in the bar, to thread the screws into.