Hey guys I'm building a 400 low deck stroker with 4.15 crank and 6.57 rods ...what piston should I use ? I've heard that the oil ring can be a problem ? It's a street car that's going to be driven a lot ....thanks

That shouldn't be any problem. You'll need a piston that is roughly 1.340 inches tall which should be easy to make. There are a lot of 1.32 stroker pistons available so you might be able to use one of them if the block has been decked. Or have a custom piston made if nothing off the shelf fits. Where did you get a 6.570 long rod? What pin size does it use?