If you want t ohave it all for the least - a typical 505" Rb with a FAST EFI and some sort of modern trans would be chaepest. It won't get the milage of a Gen III but it will look "right" and if it couldn't get high teens mileage wise I'd be surprised. The new hemis are cool but they take a lot to get in place - and nothing's cheap stuff. I'd rather have a car that's worth more than I just put into when I'm done, and a high hp gen 3 swap will be close to break even at best. The last pull out 6.1 I had any interaction in was $6500 byt itself and makes 345hp to the tire with a carb and cam swap. That's not enough steam to put a heavy E body (saddled with options and stuff) to mid 11s. Especially not with the driver shifting it and street rubber.