Well, the b17 is nearly idential to a b16 but with a longer stroke. Having that said, its going to be much more difficult to build that motor because I don't think anyone make a off-the-shelf rod that will accomodate the b17.

I would recommend just bosoting the stock block. 250whp will be easy on a stock block with a decent turbo setup. If you really want to build it, ditch the b17 block and slap its head onto a LS or GSR block.