You'll need a TV (throttle valve I think) cable and there is a vacuum adapter for the lockup torque converter so OD will work properly and not burn up the trans. I've been looking at converting a th350 to 700r4. You may be able to reuse the crossmember, not sure of the length, but you should be able to drill a couple new holes in the frame if you need to. You may also need to get a different driveshaft. I'm not sure how long the 400 is, but I know the 350 is shorter than the 700 and I'll need to get mine cut down a little. There are loads of other forums where guys have done these swaps in to older cars.
http://bowtieoverdrives.com/index.shtml these guys also have a lot of good information along with some of the parts you may need. I've never called them, but they seem to be easy to talk to if you have any questions.
In response to burnhedge, he makes a good point. You might want to have the 700 rebuilt to handle the HP and torque your 454 is putting out before you install it.
