How much pressure? How about in gear? I'm assuming the converter is turning the input shaft (and it should since it checked out). If there is sufficient pressure either reverse or at least one forward gear should function. I doubt if both servos and both clutch pistons are all leaking enough for none of them to function. The valve body and converter should be out of the equation so lets focus on whats left. There could be a massive internal leak. The only time I've seen that was when the reaction support was loose against the front pump. Maybe it's tight but fits poorly? maybe a mismatch of parts? Again that should show in a pressure check. Are the rear clutch hub splines stripped on the input? Or is the hub cracked? Does the valve body set flush on the case? There isn't a accumulator blocker rod holding the accumulator piston just high enough to hold the VB away from the case slightly? My opinion is if it has good pressure there is a hard part failure. If the pressure is low you may have to do individual air checks while dissembled to find the leak.
Doug