I'd say the performer plus cam is the the weak point in your combo and the performer intake, I'm sure those heads would make 30hp over stockers even with the stock cam, theres cams out there with 10-15 degs more duration/ tighter LCA and more lift that will keep the low end yet increase midrange and top end alot and have more area under the curve, the performer cam runs out of poop just when the heads are making power.......the edel 500 carb is not the greatest for autocross, I'd be running a demon like a 525-575 with annulars with an rpm int and some try-y headers, the 165's even t/wedge heads would probably run stronger, I would guess the regular performer heads would give you much more low end on a 289. The cam is a major "mismatch". I'd say if anything, more cam, mill the heads for more compression and better carb and headers. You can always add steeper gears and pump up mid and top end and you will go faster......way faster.