Whatever it is, I like it. That truck has to be 40 years old too, I am guessing. I am not really a chevy guy though.
As other members have suggested it is a Sireno Condor.
It is easy to spot.
More or less straight sided lenses in comparation with the TwinSonic that have slightly sloped sides.
The lenses are higher than on the TwinSonic.
Independent rotators in black plastic that rotate in the same direction in comparation to the TwinSonic that has synchronized rotators in metal that counter rotate.
Both lightbars has similar stepped mirrors that make them look similar in flash effect except that the Condor is independant and do not have the inboard to outboard flash effect because of the rotation in the same direction.
All this was probably because of the Federal patent of the TwinSonic.
Sireno could most probably change the polarity of the motor to have the lightbar counter rotate at a later date when the TwinSonic patent had run out.
I have never seen that but I have a four sealed beam Sireno beacon that have insulators on the motor so the polarity is changed on the motor that makes the light rotate in the opposit direction than original.
It looks factory installed and not home made so I think it might have been a possibility from Sireno if ordered.
Michael