I was under the impression that only Longfields needed the 40 knuckle ground for clearance, but the 60 Birf did not. To be clear, from what I'm reading above that's not the case?
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I'm not sure where and exactly how much clearance to grind. Where, exactly, is the interference?
You don't grind the knuckle, you grind the opening of the FJ40's axle housing to accommodate the birf. And you have to grind for both the longfields and FJ60/62 birfs.