Wonderful things those airhorns. I think they would be Fiamm Road Master horns. The '67 Quattroporte had two horn circuits: town and country. I think the airhorns were on the steering wheel and the small electric horn was on the button on the end of the indicator stalk. The steering wheel was a work of art, it is "signed" and could very well be a Motolita, but I don't recall. The centre horn button is also connected to arms behind the wheel that have matching wooden tabs in the spokes of the wheel. In other words you can press the tabs in the spokes or the centre button to actuate the horn.
The trumpets can be tuned to give the desired high/low tone by loosening the locking nut and screwing them in or out a fraction. You may need to put a little light oil to lubricate the air pump. If it is the same as mine was there is an oiling point covered by a cap. The pump is mounted vertically, I think the oiling point would be at the top.
You can still buy the same make of airhorn today but they are plastic. It may be worthwhile running a circuit with a switch so that you can have the original horn around town and the airhorns out on the highway. I suspect the Maserati system with the button on the end of the indicator stalk, whilst not impossible, might be too difficult.
I am reasonably sure that a relay was used as the pump draws a fair bit of power.
If you need I could ask the present owner for more information.