This really depends on the year and model of the Nissan hardbody. The best source for information such as this are any of the support forums. People have a lot of insight as far as swaps such as this. As long as you have the patience you can virtually swap any body onto your Nissan!
A fairly loaded question for sure. Most repairs/replacements on this level are not safe for novices to perform, consult your car manual or speak with a licensed mechanic before hand.
The bst way to answer that is to do an internet search for it and it will give you all the deatils with instructions that you can print and then file awat for future reference.
Many new manufacturers are now bringing good engine models for the Nissaan. But one should make a choice which will be the best fit for his car. i think sr20 will be a good wap.
The main two motors that can be swapped would be your basic V6 motor and V8 motor. Both of these motors can be placed in the car or truck and give you more or less gas mileage.
