All good stuff, thanks for all the input. So is there a difference in vacuum cans for ported vs manifold vacuum?? Say like a stock points dist. in '70 was hooked to ported vacuum correct? Are the newer distributors ie: mopar performance electronic ones, firecore, FBO, set up with a different advance unit that is designed to use manifold vacuum? or does it basically just boil down to how much vacuum your engine makes at idle and what it prefers timing wise?