I really think you should trust the ones who have been producing award winning products for 10+ years versus your own cobbling together of parts.
Don't worry, making brackets is pretty basic if you have the machinery and the know how.
I'm not saying Noctua are being incompetent, they're being greedy. They know most people will just assume the size of the IHS will cause existing coolers to perform badly and buy a new one. Like a cooler that worked fine on a 220w AMD CPU will suddenly be incapable of cooling a 180w one for no reason lol.