Per the folks on the Magnum thread in the suspension forum, you cannot fit a 29+ tire in the 27.5+ fork. I asked this exact question because I almost bought a 27.5+/29 Magnum.
Manitou makes the Magnum (now Mattoc) specifically in a 29+.
I have a 29+ and there’s enough room for my fingers between the brake arch and every plus tire I’ve tried.
I’ve seen pics of a 29x3.25 Duro Crux that fits just fine in a 29+ Magnum.
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