Because I know that the combination of parts I have laying around is not the best for what I want to achieve. I do have some very nice capable stuff but I want to do this once if possible. It's cheaper to do it that way.
I just figured be nice to work from a baseline then dial it in, I'd probably just port the heads the run the rest as is and play with cam, intake, gears, stall etc.. until I got it where I want it, but each to his own.