Those d-ports should bolt up fine. As far as wasting your time without the headers, NO, but headers will enhance many mods you have done or plan on doing in the future. Since you have a cat-back already a high-flow cat and long tubes will really open up the exhaust. As you also mentioned the intake would just further help increase the air flow. Lots would say the first place to start is headers followed by some intake work.
As far as the 113 heads.....
With some good port work alone you'd probably see about 30chp more than you've got with your current stock heads. You could also slap some 1.6 Roller Rockers and better springs to really make it worth while. A set of 1.6 RR and springs will increase your lift and give you similar effects as installing a LITTLE beefier cam without going deep into the motor and give you some more usable RPM's.
Be careful and jot down your plans and calculate the costs to rework these heads. You could do a 3 angle, port, polish, RR's, springs, seals, and labor combined with what your paid for the heads already and be in to them for almost as much as a good set of aftermarket heads that will flow better right out of the box.
At a minimum get them ported and polished and slap them in, 30chp is a noticeable difference and helps keep the grin.
Art
113 heads
Linear Mode
