Since the inline 6 crankshaft is inherently well-balanced, changing piston weight doesn't induce any nasty vibrations. I'd definitely reccomend an upgrade to aluminum. Less reciprocating weight will make the rod bearings last a lot longer and the acceleration should be better to boot - - - -less inertia.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!