ok here goes ..
im assuming you're in the states
any motor that did not come in your car is illegal, smog/emissions wise. The only motors that would be legal are motors that are sold in the states put into your car that have been through the state inspection and they put a new engine plackard on your door jam .. then the replacement motor become legal. any other motor other than USDM is illegal in US cars. ... there is no way to make a JDM/UKDM motor smog legal, the only way so it could "maybe" pass is if you pay your smog guy, hes a friend, or hes really dumb.
now about the engines...
if your car came with a GA16 , the only motor that will swap with yours is another GA. The SR motors have all the different parts as listed in the link Harris provided (ie: axles, m.mounts, wiring harness etc.) Basically the bottom line is the GA and SR motors are different. ... so your only option would be to swap another GA into your car , but if you decide to swap an SR20DE into your car, all the parts to do so are readilly available through your local nissan delear , nissanforums/sr20forum members, or the junkyard.
and FMIC = front mount intercooler /// TMIC = top mount intercooler
someone pls add/correct this if im in error
