8" Torque Converter - Strip AND Street??

I helped a friend with his 68 Dart he runs a 8" ATI 4200 with 5.13 on the street from time to time can drive it all he wants and it doesn't seem to be a problem. My son has a 426 small block with a 727 8" ATI 4500 converter and 4.30 gears and it works fine on the street.