Can't tell you specifically about the 76 models but in 73 the 440 was down to three levels of power (215, 220, and 280 hp.) That said don't worry too much. The heads will probably be 452's with 81.5 cc chambers which won't be too bad. Earlier castings might be a bit better and have smaller combustion chambers if you feel you need them. When it comes to the crank it's a crap shoot since Chrysler used both cast and forged cranks in 76 so you won't know till you tear it apart.
When it comes to building HP the 440 is a great starting point. If you're going to rebuild it anyway you can simply slip in a new set of pistons to bump up the compression to around 9.5 or 10:1 for a street motor and the rest is just replacing what needs it. If you plan on any racing I would definitely make sure you use a forged crank.
$500 is a good deal.