Maybe you can calculate them like what I did.
For example, when you get the following expression,
Out= -2 (4 (m2 m4 - p2.p4) 2 p3.ep[p1]) p3.ep(*)[p1]
replace ep[p1] by LorentzIndex[mu] and ep(*)[p1] by LorentzIndex[nu], and then multiply the expression by a tensor which is the sum of polarizaion (maybe it is MT[mu,nu] or something else).
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