The 700 is a considerably lighter-duty box than the 400, but it's got overdrive and a lockup torque converter. There is a modern, overdrive-equipped model of the 400, don't remember the designation, but I think it's computer-controlled, and it's a tough swap to make. GM uses it in their motorhome chassis, behind the 454 engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!