Here is a picture of the factory horns and brackets from the 1951 Accessories filmstrip.
http://good-times.webshots.com/photo/2465676350102454676PdnAfU
I have had two sets of factory horns on earlier trucks (48-mid-49) with a one piece bracket and the firewall relay correctly installed.
http://rides.webshots.com/photo/2879999230102454676CXAeoJ
Compare and see the horns should also be marked with L & H for high/low tone if correct.