Power Valve #'s

I understand dividing vacuum by 2 and adding a point to get the magic #, but the p.v.'s are marked as E 3 5 6, and E 8 5 0, and # 8 5 8. Three #'s, not two. It seems the Higher the #, the more pressure it takes to close the p.v. w/ your fingers, the one i have in the primary side now is even weaker, so i presume it would be a E 1 4 8 or something like that. Maybe my vacuum gauge is broke or something, but in gear at idle, i'm measuring about 6hg... the cam lumps like a sonofa though. (mystery cam) 3.5 = ?; the E 3 5 6? the plugs are reading way too rich city driving around. i imagine the weak spring rate pv in there now is letting too much gas in?

The real question is, if i need a pv rated for 3.5, how do i identify which one i should use via the #'s stamped on it. Would i use the E 3 5 6? Is that the closest one to a 3.5?