how to find out the stall of a converter??????????????pic included

I would take it to a tranny shop,to have checked out.I know from my experience building my engine/car we had ordered the torque converter(4500 stall)to match my camshaft and gear ratio/tire size.Hope this helps.

Oh by the way,mine is a 8 inch Coan 4500 stall,yours looks similar in size.
View attachment car pics 66 Dart 142.jpg