Stock Air Horn Compressor size

[Det57]

I have the factory (I believe ) air horns on my C50. Two horns on the roof. The air hose comes down through the roof and ends behind the rear seat area. There is no compressor.

I would like to get one to try and get the originals working but not sure what size to get. I don't want to blow them out. Does anyone have these on their truck and can you give me an idea what size compressor to get and where is yours mounted?

Thanks