Differentiating between 700r4, th400 and th350?

My cousin asked me to help him figure out what tranny he has in his 79 chevy truck, but I couldn't tell him. Just looking at it from the bottom, is there a way to tell?

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I am speaking for what is normally in them here. First off I am assuming that the tranny in there is original. That being said, it is not a 700R4. Easy way to get rid of the 700r4 is see how many forward gears it has. If it does not have an OD then it is not a 700R4. Plus a 700R4 was not used until way after 70 in pickups. Also, what kind of motor is in it? Normally then th350 was in all small block chevys. The th400 did the job in the big blocks and all the 1 tons. Someone correct me if I am off but this is how I have always seen it.

Let me break it down for ya:

700R4- 4spd w/OD, square pan
TH350- 3spd, sqaure pan that looks like 1 corner is cut off
TH400- 3spd, pan almost looks like a blob (sorry for the poor description on this one), basically its not square like the previous 2

Hope this helps

http://www.nastyz28.com/transid.html shows the different pan shapes.

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Thanks everyone. I will probably check on it tomorrow.