I saw an article awhile back in one of the magazines about building a 350 SBC versus a 454 BBC. Their opinion was that for the money spent, the 454 BBC didn't really make that much more power than the 350 SBC.
Personally, I would build the 350. I'm not so concerned about the weight, but I am concerned about the cost. I hate to see people spending millions of dollars and not get the power they could have with a fraction of the price they spent.
I may be wrong about this as I don't really follow Nascar, but don't they run 350 engines punched out to 355? They seem to go plenty fast and don't run big blocks. Granted, they need the lightness of the 350 where as you have a bigger car.