GM Turbo 350 Fluid leaks

[GEF56]

Im putting a chevy 383 stoker in my 56 truck with a GM turbo 350 and have been filling it with Automatic Transmission Fluid for the first time. I followed a number of posts which recommended that I First put in 4 quarts and start the engine in park and let the fluid circulate for a few minutes. This was fine. Then the posts suggested adding another 3 quarts start the engine and start checking the fluid levels while running . Still went well. Then it suggested you put it in reverse briefly and then through the other gear settings...at this point fluid began to run out from the torque converter cover. Help and ideas or suggestions this is my first automatic transmission.