torque converter how to order

Rapid Robert said
63 dart 360/904 dirt track stock car. I want better than the OE unit in there now. How should I go about ordering one? Idle rpm? RPM coming off the corners or? thank you for your time. and what company would you suggest I deal with? RR

Call several and over the phone describe your setup and desired outcome

Precision of New Hampton in Iowa
Biltron in New Jersey

Others will provide options I'm sure... but a conversation is the best way to go.