I need to by a Tranny A604 ( 4 speed). They asked me wich one!!

the one with internal neutral pin - Round pin.
or the one with flat pin!!

How can I know wich one is the one that I have or need??

 

You don't say who "they" are so I figure you're dealing with a parts store.

It might be better to have your tranny rebuilt locally by a reputable shop than replacing the whole thing with a factory rebuild.
The national chains usually just roll out the old tranny and roll in a rebuilt part off the shelf.

 

Remove the TRS connector and look at the pins. Its either round or flat.