I'm somewhat floored by urge to make a billet crankcase; but motivations are perfectly logical. I imagine it'll be undertaken via CNC? Billet cases have perfection written all over them, right down to modifying drainage tracts, fixturing pads, ultra clean fillet & radii, ad infinitum. Fixture pads would aid line boring process with permanent datum. Not to mention increased strength from cast 356 to rolled 6061. If you've ever worked 7075 though, it may prove even more superior, and the finish is spectacular!