I wouldn't try and build a high HP(over 650 HP) race stroker 440 block motor if you have a 400 block to start with You can make a 400 block stroker motor have the exact same cubes as the 440 block and shoot for the moon on HP and RPM and not have to worry about the weak main webs commonly found on all stock Mopar RB blocks Put a decent set of either Milidon ductile iron main caps with main studs, no girdles,or some brand of aluminum main caps and main studs on the 400 block and go racing With your heads I would build a 4.250 stroke 400 block and the compression ratio you want to run, shift it at or around 5900 to 6500 RPM and go through the 1/4 mile at or close to 7000 RPM