With a good set of heads you can get that from a 440 on pump gas. You need to feed the bigger strokes, so expect to spend some on heads, cam and intake. You don't want to run a purple shaft... run something by anyone that was designed in the last 5 years, and run it around 250°@.050. That 870 is small for a 505 (which is the 4.25 stroke kit in a .030 over block) For longevity, dont use a piston shorter than 1.45" adn it will last. Plan to have your shop balance the thing, and expect to have the rods corrected and the crank carefully checked.