As has been said already, heads would get you the most power, but would be $$.
Bang for the buck? I would go with a 4.5" crank and 7.1" rod. More power especially at shift recovery, lighter bobweight, and not much $ when you sell your old stuff.
Plus would be a better foundation when you finally upgrade your heads.
I agree that would be great to get a rew more cubes.
My current crank is a Crower center wieghted piece , replacement cost over $2500, best steel short of billet (en30b?) Rods are 849 gram hbeam 2.200 journals, so not a lot to gain? Since i am going aluminum block that center wieghted crank may aid in less cylinder distortion and better ring seal.
