I can give you a partial answer Paul. The 58 box has the one piece shaft, the horn wire runs outside the shaft, and I think with the 58 wheel it will stick up more than the 54. I have never seen this done in a 54, but I know alot of guys have used it in 57's.I am working on a setup for my 57 Custom now that I hope works out OK. I am using a gear from a 64 Galaxy with a colume from a 73 F100 with aftermarket wheel. I have all the parts, just waiting until the new shop is completed to get the frame back inside.
Maybe someone else can give you more info on using the 58 box in the 54.