I have considered building a unicycle as well, including the Nimbus brackets you mention. It looks like blades using these brackets transition from round to ovalized and pretty narrow at that. The brackets are listed at 22 x 42 x 12 mm. I always took that to mean 12 mm wide. Not a lot of real estate to work with. I have never found a straight forward method for ovalizing tubing (that still looked good when I was done) to this extent without a lot of effort. I have pictured machining some unicycle specific hooded dropouts to account for this (that would allow use of round tubing or unicrown bike fork blades) but have not pursued it. I would love to see how you have progressed on the project.