I had my 727 do that same thing many years ago. Oil came pouring out the bottom of the bellhousing after a pass at the track. It was a cracked converter hub. It was not visible to the eye. But I stuffed a rag in the conv snout to seal it up around an air hose and applied air pressure to it. It showed all kinds of bubbles coming out of a crack that started at the sharp corner on the drive tang.
Had the snout replaced and took care of it.