You're missing about 30 years of context. Doug has built hundreds of slant-6s of every description, has devised numerous improvements and fixes for them, and almost certainly has more experience with the aluminum slant-6 than anyone else alive. He didn't run nonstandard clearances by guess and by gosh because he "thinks he understands" what he's doing, he did knowing fully well what he was doing, on a block in marginal enough condition that he didn't feel bad sacrificing it for the sake of experimentation.
