If you stay with a stock block the life of the block can be increased by using a centwr wieghted crank. That puts the loads where they belong , not on adjacent main bearings. To put one in a b block will take some machine work. Since you want to push it fairly hard, i would go lowdeck 4.25 stroke by 4.375 bore for 512 cubes. Isky grinds some very good cams.check out thier . 660 lift roller, maybe put a 1.6 rocker on the intakes. I would go with a solid roller, about .700 net lift roughly. A single dominator and 2 1/8 headers. Compression will have to be as high as pumpgas is allowed.