Actually, with a die grinder and a little patience you can easily and cheaply make a noticeable improvement in your power. All by yourself....Match the plenum intake to your larger throttle body and smooth and polish that throat as best you can. On the other side, open up the intake runners as best you can,as far back in as you can, and grind off the big bumps where the injector screws go in. You may have to put the injectors in and trim the screws where they protrude into the runners. Polish the runners too, as deep into the plenum as you can reach. Now smooth out the intake ports in the head, going after casting bumps and sharp edges. With the stock manifold, port matching or enlarging the ports won't help you much, but smoothing bumps definitely will. Polish the intake ports and then rough them up again with 100 grit after you get the bumps out. Pay particular attention to getting all rough spots, sharp edges, and bumps off the short side radius of the port...(the inside of the bend that the air has to flow through) In the valve area, being very careful not to knick the seats, smooth the transition from aluminum to valve seats, and in the combustion chamber, unshroud the valves so you have 3/16"clearance between the edge of the valve and the side of the chamber. (Be careful not to grind too far; use a head gasket to mark the limit of grinding.)Mirror polish and smooth as much of the exhaust ports as you can reach, but don't try to get the liners out...they don't harm flow as much as you would think, anyhow. Mirror polish the tops of the pistons, and the inside of the combustion chamber, and smooth any sharp edges, and extra threads for the spark plug holes. (Put a plug in and see where there are extra threads caused by the tap at the factory, past where the plug protrudes into the chamber.) Since you have the head off, see about having a new valve job done.....SI hi performance swirl polished valves cost about 14 bucks apiece, and a modern shop with CNC equipment often does a 5 angle grind for about the same cost as a 3-angle. Anyhow, if you are trying to do this on a tight budget, lap the valves lightly by hand, and put it all back together with a felpro gasket set, which will raise your compression slightly over stock. Replace your valve seals, they come with the felpro set. Borrow a scale from a drug dealer and lighten, balance and polish your rocker arms. Finally, if you are not putting on a header, do what you can with the exhaust manifold, smoothing and polishing the ports and runners. Do not try to port match your exhaust.
You can do all this work yourself, and all it will cost you is time and abrasives and a gasket set. it's hard to say how much you get from every little bit....but after you are done, you will definitely see a power improvement. With the polishing of the chambers and piston tops, and the removal of threads and sharp edges in the chamber, you will be able to advance your ignition timing more without getting pinging problems. If you don't do this, then you won't see all the power increase you are looking for!