The duration at 50 is a good range for your converter especially considering it being installed at a 107. Now if you go with a higher stall converter I feel you will be disappointed with top end power. If you go with a 4500 converter your duration at 50 should be 265+. And you will hate cruising the car. It'll feel like you have to mash the pedal when taking off from idle at a stop light.
The car seems to me with gear, converter and cam to work well as it is on the street. If you want more top end power retard the cam 2-4 degrees, if you want to fry the tires advance it 2-4 degrees but it'll have its tongue out quicker on the big end.
