For your application Im thinking you wont see a difference. But Mikes right, smaller mains, less resistance, bigger bore, unshrouded air charge.

I used a 360/408. I hade a block, I used it, I would have done same thing VS a 340 block but I didn't have one Id trust.

So.... 408 for me only because its what I had. I have a K1 crank, and Indybrock heads. 602" solid roller, and I LOVE IT!!!

Its really fun in a light A body.