Go to 25. Grade 8 should handle 30, but why push your luck. 26 is the low end for the grade 8 I believe, so you should be OK there too.
Yoke should be very tight, so 175. It only tightens up the compnents on the shaft, and does not effect the bearing preload. That is controlled by the shims, and you are working with worn bearings anyway. We usually held the flange with a holding tool, because getting the proper torque didn't work as the engine would simply turn over. The reason the nut was loose was likely that the last guy installed it with a weak impact gun, or hand tools that were inadequate.
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