The stock Gen II Intake manifold produces FIFTY more ft. lbs. of torque between 2800 and 4000 than the stock Gen III Intake.
A longer runner with no taper tunes harder at peak torque.
There is no increase in peak horsepower over the stock Gen III Intake.
To convert you'd need (2) TBs, proper linkage, a revision to the thermostat housing (like from a Viper car), fuel line routing, some kind of air intake system and a "custom" upper rad hose.
The Gen II also used lower capacity fuel injectors than the Gen III.
The o.e.m. Gen III Intake was a Lambo design and was more for form than function.
The Gen II is a better manifold comparing each, unmodified.
The Gen III Intake can be modified to work quite well but it takes a considerable amount of time and effort..
Ronnie