904 or Powerglide???

Personally I would consult the torque converter manufacturer for recommendations on the converter. If you go with a reputable company like Coen, Turbo Action, Dynamic, ATI or A1 they'll know what would be best. If like Moper said you have the dyno information that would be even better but they can get close with basic info like head flow/manufaturer, intake, camshaft and so forth.