Mechanical (slot) timing (or initial timing for that matter) does not alter phasing, only vac adv does. with no vac adv if the rotor is moving it is due to lower shaft tang/intergear notch slop (or the rotor is loose but they tend to fit pretty tight). With no vac adv being used it's easi(er) to alter/set phasing, on your bench just pump up the can slowly till the phasing is dead on then take the dist to your drill press with hand pump still attached & drill down vertical thru the 2 plates in the right spot then dissassemble & clean everything & lock the 2 plates in that position with a mini bolt/nut with a sleeve on the bolt inbetween the two plates so you dont tilt em when you snug the bolt. With vac adv I like the sweep to be equal on either side of dead center and with a hot eng with it possibly being a little bit closer in the no vac position as that is what it is going to be at at WOT (little/no vac) when required voltage is the greatest & that's when you'd want the least amt of gap. Getting that NAPA rotor with the longer blade is beneficial as any gap outside the plug gap in the combustion chamber is a waste of energy & ups the requied voltage to jump that (excessive) gap. Yes some dists have phasing a mile off. If the intergear slop is allowing the rotor to move say 2 deg up top then that means that the timing can adv/retard 4 deg at the crank at will. EDIT if you are pinning the plates and you need to shift the phasing the other direction (CW on a SB) you can unhook/remove the can & manually move the plate till it's phased, just dont go so far that one of the (3) pedestals is uncovered cuz the plate needs to be supported by them