Here are GM RPO's on transmissions from my near 25 years of playing with my Monte, hope it helps.
MM3 3 speed manual, MM4 4 speed manual, MT1 THM-4R O/D auto, MV4 TH350C, MV9 TH200C, MW9 TH200 R4, MX0 THM O/D (4 speed), MX1 THM auto (3 speed), MX2 MX3 MX5 TH350C, MY1 4 speed manual, M15 M16 3 speed manual, M20 4 speed manual, M29 TH200, M31 TH250C, M33 M38 TH350, M40 TH400/TH375
MM3 3 speed manual, MM4 4 speed manual, MT1 THM-4R O/D auto, MV4 TH350C, MV9 TH200C, MW9 TH200 R4, MX0 THM O/D (4 speed), MX1 THM auto (3 speed), MX2 MX3 MX5 TH350C, MY1 4 speed manual, M15 M16 3 speed manual, M20 4 speed manual, M29 TH200, M31 TH250C, M33 M38 TH350, M40 TH400/TH375