Not sure if I’m missing something but here goes,
The beer gutter layer is 3/4″, the final top layer is 3/4″ = 1 1/5″
The specs on the Kegworks arm rail says the rise from the base layer to the final layer overlap is 1 1/4″
Sure I can add some 1/4″ sheathing or ? to the 3″ base layer overhang to make up the difference is this the way to go.