Well, since I don't want to run with anything larger than BBC journals, the billet piece is out.
From the info I have gathered, I have learned that 1) aluminum rods will not clear the cam with crank strokes longer than 4.500" and 2) crank strokes longer than 4.500" will cause excessive piston skirt wear.
Interesting enough, I have read somewhere about a new piston being made with an asymmetric skirt, favoring the major thrust side. Maybe just for this kind of build.