The TC is simply the larger car. The 258 could be used on the Imp trans or the 245 flex could be swapped to teh Bonne. That'* the easy part.
2004 requires a different type of control than 2000. I'm not 100% that it'* a direct bolt in and go. Check the Tripleedgeperformance.com website for more info, maybe give Dave a call. (tell him I sent you). He'd be the guy to know if it'll work.
other than that.. take a look at the back of the trans casing on the impala. Does it have three-four holes for bolts or only one?
You need a casing with this webbing/holes
You can not use this cype of casing