mostly US-DOT regulations for emissions is the difference between anything not in the US market. things are more strict here.
so everything that goes along with that is changed, detuned, more restrictions to airflow from things like cat. cov. noise levels are a concern as well etc.
JDM is usually just a buzz phrase for ricers.
HOWEVER, because things are different over there, its possible to find the cars with low low mileage, so for a swap, thats ideal. try finding an MR2 in America with 50k or less miles on it. there are also small styling differnces maybe differ headlights or taillights. small things like that which you may find you like better on your car than what was put of for the US market, but thats just personal preference.