Street machine converter - 3,500rpm stall?

how can you tell what stall converter you have?
Stop the car and brake torque it up to as high as it'll go and look at the rpms and that's what the converter stalls in your car. That may not be what it's rated at but that's what it stalls in your application.
And how can you tell if its a loose or tight stall?

Like mentioned above a tight converter will drive pretty much like a stock converter. A loose converter will slip quite a bit until you reach it's stall rating.