I'd try to get your hands on a Pontiac 400. Those are hot engines, and aren't a bank breaker to buy, nor run. It should be a good fit for a car that size & weight. Not hard to make fast too, as there is a lot of performance parts available for it. Any wrecker should have a good old one, then you can have it rebuilt or do it yourself for a few thousand. Like I say modding it isn't hard to do to get decent figures out of it. Much more so then the GM 400.
While the 455 is an incredible engine, not too many people can afford to use them with todays gas prices.
The 455 (if you read up on it) has an abundance of Nascar technology stuffed into it. It was pigeon holed to conform with Emission regulations, but with just mere bolt ons it can sing and put out some impressive HP numbers, while still being very much stock. Kind of too bad though, as awesome of an engine as it is, it'll drink the gas no matter what you do to it. I forget what that "455" translates too, but I think its around 7.2 liters.