Torque Convert Experience

My father in law has a 380hp 360 Magnum Crate and a 904 trans in his 69 cuda. He currently has changed his gear to a 2.94 due to the fact that his race days are over and he just wants to enjoy the ride. The torque converter in it is a 2600rpm tci and he is wanting to go down to around a 1200 converter as you can feel it slip with the new highway gear in it. Anyone know how this motor would act with a lower torque converter? Mopar suggested a 2200 at least but I find that a little hard to believe since the cam is pretty mild.
Thanks for the input