The best mod for more hp for your Mustang is a split port swap.
96 single port 150 hp 215 tq
99-04 split port swap.......... can be done to your engine 190 hp 210 tq
Windstar swap with split port lower intake 200 hp 240 tq
new pistons will help with the 10-15% hp lost over time
new engine,1.7 rocker arms,Pipes exhaust, shorty cats , shorty headers,under drive and overdrive pulleys,4.2 upper plenum, throttle body spacer, cold air intake, stage one clutch, shorty shifter, and tune. 8.8 in storage