[mgarblik]

To me, using a "557" 400 block in place of a 350 Pontiac is a no brainer. Even though pistons are available for a 350, at a greater expense and effort than a 400, what do you have when your done? A 350 Pontiac engine vs a 400. Even with a very mild build, you are giving up 40-45 "free HP", by virtue of the displacement. More importantly, you are giving up 50-60 Ft. lbs. of torque, power you can feel seat of pants. The physical engine size is the same, so why build a 350? To keep a numbers matching combination together or because a specific race class requires it would be the only reason to keep the 350 IMO. Gas mileage improvement would be in the 1 to 1.5 mpg range if that's really a consideration. The 557 block is not the best 400 block, no question. But for a 400 HP or so stockish build, I would have no issue at all using one. I would think you would enjoy having the very real increase in power with no downside. Good luck with the build.