Guess you've never talked to me. If I were to build the 340 in my Duster again I'd drop the compression ratio half a point, drop the cam down a step, and make my daily driving habit a lot easier to deal with. 350 to 400 hp in an A-body is plenty fun on the street and still everyday drivable. 800 hp in one of these cars makes it a trailer queen. Put 10k+ miles a year on it, drive it in the rain, in traffic, in 100*F and hotter weather, you won't want that 800 hp engine for that. I loved driving my Challenger for the 70k+ miles I put on it, it was just a plain jane 318 with headers and a 4 barrel. Fast? Not really. Still lot of fun though. Just depends on what you're doing.
As for the OP, unless your plan from the very beginning is to absolutely max out your tire size for the body there's no big mistake. You can't make up a 1/2" in the front anyway unless you actively push the fenders out, and even pre-bodywork doing that changes the lines of the car. You can see the bulge in the fenders from when I rolled mine. Yeah sure, in a perfect world it would be better to sort all that out before you start painting stuff, but unless you're willing to cut and push the bodywork it doesn't matter anyway. Lots of folks don't want to cut their cars to fit the next up tire.
