I think ...
I think you would be better off to focus on building the plane straight and true then adding ballast or shifting weight to get the CG where it should be. CG is a very static thing with empty tanks which is the way I did the weight and balance on my RV-6A. Fuel is a preflight calculation just like everything else loaded in for the flight. The tanks are fairly close to the for/aft CG so it will not cause a gross shift. Anyway, that is pretty easy to deal with but if you get paranoid about this and start changing other areas and mess up the alignment and fit of the engine, alternator pulley, crossover exhaust, baffling, spinner, cowl, airbox, nosegear structure (on "A"s") you can create problems that will be around for a long time.
I have the small pulley on my alternator and I still required a steel striker plate to protect the cowl. I had to cut off sections of the exhaust pipes under cylinders 1 and 2 to get clearance from the cowl (this was caused by a cowl design change by Van's that Vetterman was not able to check for compatibility before incorporation).
Bob Axsom