i have a set of 30 over trw forge flat top pistons l2256 but i can trade my old block and them for 30 over keith black dome piston and scorpians roller rocker wat should i do

Depends on a lot of factors.

What do you have for a block?

IMHO, you're getting the crap end of the stick if it's a good 350 block and you are getting weaker pistons, and $150 worth of roller rockers in exchange for forged pistons and a good block. Not trying to be a dick, just my opinion.

thats only a 2 bolt block 3970010 and the block i want to use is my 4 bolt stock block 14010207

What exactly is your (realistically) intended usage of the car? Hot street car, road race, plain jane rebuild, drag?

The 2 bolt block would be fine for most anything shy of large doses of spray and constantly higher than 6000 rpm. If you need 4 bolts, I'd assume you'd also need forged pistons, making the KB trade a negative.

what i will have is 30 over 350 4 bolt with vortec 062 head roller rockes voodoo 60103 cam flat top pistons edelbrock rpm intake and 750 carb i was told that with this set up should have about 350 to 410 hp which im good with

With Vortec heads I'd stick with flat-tops. The domes probably wouldn't even fit up into the chambers and would hit; and the compression would be too high even if they did fit.

The 2-bolt/4-bolt thing is negligible. Factory 4-bolt setups aren't any good as reinforcement against "high-perf" type of stress, which is RPMs. That's not what they're meant for. Personally I wouldn't pay an extra dime for it.

Stick with what you've got if it's in good shape.

i have them both in my house i got the 3970010 for free so i have nothing into them and i will wana go to a 383 stoker in the future just not right now so the four bolt will be strong i was told by my uncle which builts motor for nascar

A factory 4-bolt block is no stronger than a factory 2-bolt one. In fact, I'd rather have a 2-bolt one if I was going to build something SERIOUS, because then it's easier to install REAL 4-bolt caps, with the 2 outer bolts splayed. Having the factory's holes in the way just makes that tougher.

Like I said though, I wouldn't get to wound up about it for street use, one way or the other. Other things about the block are MUCH more important; like, if all the factory machine work is right. What the factory 4-bolt setup does for the motor is of no value for our typical intended abuse (high RPMs); and what a motor subjected to our form of abuse needs, the factory 4-bolt setup doesn't provide. It's nice and romantic sounding, and everybody seems to want it especially people with no experience except for lots of time listening to ratchet-jawing in the McDonalds parking lot on Friday nights, but it doesn't make a hill of beans' worth of difference to the finished product. Not better, OR worse.

DITTO on the 4 bolt versus 2 bolt question. In fact, for NASCAR, when using an OE block rather than a Bow Tie block, the 2 bolt is widely preferred by those of us in the know because it is actually slighlty heavier in the main webs and with splayed caps makes a stronger bottom end.

Flat top pistons with 64cc chambers will produce about 10:1 compression. You will not want to go any higher on pump gas.

As far as forged versus Hypereutectic, forged on the street is overkill and can be a little rattling. "Rattling" literally on cold starts until the forgings warm up and swell to fit the cylinders. The added strength is not an advantage as the Hypers can handle anything you will throw at them, up to atleast 600HP, including nitrous and boost. In fact the Keith Black Silver Eagles are about as strong as most forged pistons. They also dont knock on cold starts.