One of the easiest ways to identify an Automatic Transmission is to view the oil pan.  Click any of the below pictures to view full size.

GM

Notes:  If a transmission has a suffix of “C” on it, (i.e. TH350C) this designates the transmission has a lock up torque converter.  This is primarily found on transmissions newer than 1980 and can be identified by an electrical connector on the transmission case.

MOPAR

Notes:  The 727 is the ONLY automatic transmission that bolted up to a Big Block mopar.

The bellhousing on the small block engine is different than a big block engine.  Therefore a 727 connected to a 340 will not bolt to a 383.

FORD

Note: The C6 is considered a heavy duty transmission and is preferable in high powered applications.