Scott, Here is a good article with pictures from Jim Carter on 1948-53 Horn bracket locations and types. The pictures should help you see how it gets mounted. As others have mentioned, the offset bracket is the one used when an oil filter is installed. Your intake manifold looks to have the horn mounting tab on the forward runner (just behind the front oil filter U-clamp).

~ Dan
1951 Chevy 3 window 3100
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