Which Transmission

I have a 1991 Dodge Dakota with an automatic transmission. There are no marking on the transmission that I can find. How can I determine which transmission I have?

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fat tail housing (about 8 ") or long and skinny (about 4 ") ?
if fat, you have overdrive
is there a bulge on the right side of the pan rail right where the dipstick goes in ?
yes = A727 / 518
no = A904 / 500

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A727 = 3 speed; A518 = 3 speed + OD A904 = 3 speed; A500 = 3 speed + OD

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