There are definitely pro's and con's based on the donor vehicle. Since you are just starting, make sure you get the JTR book as it will answer a great deal of your initial questions.
http://www.jagsthatrun.com/Pages/Datsun_Z_V-8.html
If you want to go LSx, here's another resource for you:
http://www.brokenkitty.com/zcar/zcar.htm
Searching on this site will give you ton's of information regarding engine choices, so make sure you find plenty of time to sift through all the information.