Flexplate or converter? What stall?

I am going to decide on the tranny before I buy, and before I put the motor in. It is going to be driven as a fast street car with the occasional trip to the track. When the motor was built, the dyno sheet showed 491 hp and 528 ftlb of torque. Since then it got the super victor intake, a new carb and rejetted a few times. I expect just over 500 hp. I do know a guy at a converter company I could call, but the opinions here mean more to me because there is a lot more personal experience in this forum, and I love to hear all the differing opinions! :-)