Street Cruiser, Do I Need a Custom Torque Converter?

In short, IMO, No.

You wrote you have a cam of “204” duration. Be it a duration of .050 or advertised, the stock converter will work IMO. For a pure driver, like you described, it is a very small cam. It shouldn’t need a special converter.

The largest cam I myself will run with a stock converter is with a duration @.050 of 218. Going larger in duration may require a bit of stall in the converter if the car is heavy and/or the gear ratio numerically low. Also, if the intended purpose is to get the vehicle going as quick as possible. Like in a street beast or bracket racer.