That style of dual horns (hi-note and low-note) was a GM accessory from 47-53. They were often attached near where the heater motor comes through the firewall.
They look right but it would be nice to see the mounting brackets and the other side of the horns, to determine if they are the GM accessory horns. Dual car horns were similar but they sometimes had different mounting brackets.
Here are installation instructions from 1951. 
