The smaller ports would restrict flow leading to lower numbers. As far as runner length, well a longer runner creates more low end torque and restricts top end whereas a short runner intake favors high end horsepower and less torque down low. The bottom line is that using an aftermarket intake such as dorman will lead to less power.
For what its worth my old 98 p71 had a dorman intake and you could feel the loss in the powerband. Torque wasnt as good as factory and top end suffered quite a bit. At highway speeds it lacked any power.
07 Gt Tungsten Grey
Roush (Airaid) Cai, GT500 Tb with BlowByRacing Adaptor Plate, UPR O/r X Pipe, M80's, Pypes Muffler Delete Axle Back, Sr Performance Adjustable Motor Mounts and Steeda Tri Ax Short Throw Shifter
02 Gt Mineral Grey
Steeda Sport Springs, 3.73s, Pro5.0 Short Shifter, Pypes O/r X Pipe, full 2.5 inch exhaust with M80's, 75mm Tb and C&L Plenum
87 Mercury Grand Marquis