ive heard from multiple people on grandamgt.com that its a underdrive also, and lighter even than the ffwd one, thats why most are leary of it not being able to absorb the harmonics of the engine. i know its a balanced engine, but you'll never feel a vibration even if its out of wack.
i would think a shop would be a cheaper option for P&P your heads, wouldn't it?
im way behind ya on performance, i just ordered exhaust though! lol