After about 30 years of the horn being secured to the engine intake manifold, it was moved to the radiator core support in 1954. This was also the same year the 235 six cylinder engine was introduced in trucks.
The actual body of the horn was used for the first time in 216 engine trucks in 1953. This horn used a different mounting bracket so it would still secure (for the last year of the 216 engine) to the intake manifold.
The radiator core support in 1954 had two holes on each side. One for the standard low note horn on the left side and on the right side the accessory high note horn. The attached photo will show the factory installed horn on the left side paired with the accessory right side horn. The HI and the LO is molded on the die-cast of either horn.
For the Real Perfectionist! In only the first year of the 235 engine installed in 1954 on the intake manifold, the cast iron horn extension was continued as the 216 engine but the two attaching holes were not drilled or used.