Just to be safe, be sure to use the sensors for your new throttle body that were on your old 2.5 throttle body. Some people have idle issues if they use the 4.0 sensors. You will need to change the housing on the ais motor to use the old sensor. All you do is take off the housing from the 4.0 body and replace it with the one off of your old throttle body. If you clear your computer before your swap, it will readjust to the new body in a little driving.
A lot of people say using the spacers cause a "whistle" sound coming from the intake. If that doesn't bother you go for the spacer. If it does bother you, I don't think the spacer makes a whole lot of difference.
The other thing I did was to take the restrictions out of the intake and output side of the stock air filter box if you are still using it. That allows more air to get to the throttle body.