The throttle body adds a little to the plenum of the intake, and lowers the harmonic frequency of the intake system. The left and right sides are different to begin with, because one side goes under the other, and has a lower frequency than the other to begin with (I think the passenger's side goes under the driver's side). By lowering the harmonic frequency, the compressed charge will get to the valve at a little lower RPM, and the torque curve will reflect that by showing up at a slightly lower RPM. The actual torque will not increase noticeably, and your HP will not change noticeably either, you will just feel it a little sooner. To figure out the RPM it will affect, you have to determine the frequency of the intake, and determine which pressure wave will arrive at the valve when it opens, giving you the RPM when the charge will help the engine. It may be as much as 300 RPM lower.
Another change you can make is to put an extra gasket under the injector tower to open up the airflow through the TBI.
Removing the air injection pump and rerouting your fan belt can remove some parasitic drag.
One of the best HP per dollar increases you can get is a set of headers and dual exhausts. You can pick up about 30 HP without any other mods. You can get a muffler hanger from the right side of any TBI car, and bolt it to the driver's side (the holes are already there). If you are going to use full length pipes, you need the heatshields from an LT1 car for the tank, or use header wrap on the pipes. I also wrapped the headers to avoid melting wiring, and the ignition wires (plug caps). You will have to make a few other mods, but the cost to install in minimal.