Stock compression on a 67 HP440 is 10:1 isn't it? So even with it being a little lower from being bored it should have plenty enough compression to make good power. I would get the make/model of the piston used for the build. If all the parts check out then I would look a cam/valvetrain issues, something as simple as rocker arm adjustment being too tight can rub power and really make it lazy on the big end. You gotta know what is in your engine, how it works together and how it is set up.