I believe that a 2 bolt 400 has 2 fleeze plugs on the side, and a 4 bolt has 3. I may have that backwards, and I'm too lazy to go out and look at mine. Anyhow, 400s have both 2 and 3, so that's not a good test. Definitely try to see the casting #s.
Mike
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71 SWB Stepside
SB400/TH350
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