Where are you located?
The only problem you have now is finding a transmission and flexplate/flywheel that would fit in the Impala. I think the combo you got out of the truck has the big flexplate which is going to cause problems with bottoming out in the impala. Most cars ran a 12" 153 tooth flexplate, Your trans out of the truck has a 14" 168 tooth flexplate. But with a little adjusting it could be a screamer. It will definitly burn your tires off real quick.
Not sure if 63 was the first year for the 409 BBC in the impalas or not.
http://www.chevytalk.com/ would have more info on the impalas. But don't leave here with out telling us what your intensions are with the truck!