I have seen some people saying they had a ported throttle body and plenum.
I will tell you what I did. Good news - it was free. Bad news - there was no OMG feeling of improved torque. But all I did was smooth out the casting lines in the inlet-elbow using grinding bits and an electric drill. I had the piece off the car working from top and bottom, as it went I kept blowing/washing out the aluminum dust. In the end, it visually looked freer flowing and I think my car has good throttle response - but that's all I can tell you. You may get more results with paying someone with experience and the ability to measure the flow before and after.
96 GT - PI Intake & cams, O/R h-pipe, Flowmasters - 40s, Short Throw Shifter, 3.73 FRPP gears.