Reversion, and other imaginary elements

Rev3[a_] := {a[[1]], {a[[2, 1]], a[[2, 2]], a[[2, 3]]}, {-a[[3, 1]], -a[[3, 2]], -a[[3, 3]]}, -a[[4]]}

Rev3[a3]//MatrixForm

( {{a0}, {{ax, ay, az}}, {{-aix, -aiy, -aiz}}, {-ai}} )

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