help identify this transmission. Supposed to be A518

Thanks
The only numbers on it are stamped in.
They are 1785 and m642
Also thereis a AA stamped

The code 642 is for a lockup, 11" diameter converter. For 360 engines. It is rated as a low stall converter, with a 91 gram weight on it. The stall speed (which can be debateable) is around 1600-1700 rpm. Watch out for the mounting bolts as they are offset.