I'm a newbie so excuse my ignorance. I own a miata and some of the 2nd generation parts are interchangable with the miata, like the AFM,

the "rear end guts" and "transmission guts." Here's a website for more detail if your interested... www.solomiata.com

I took a trip to the junkyard looking for AFM, injectors and hopefully turbo LSD. From what I know 86-92 have same body style right? if so, how can you tell if it's an 88 or earlier?

One more newbie question... only looking under the hood 2 times, can some one direct me to where the injectors are, maybe a picture?

Well a really noticable thing is the tail lights the 89+ have a round style while the 86-88 don't. As for the injectors, I'll let some one else handle that one i would probably confuse you.

Looking at the body it is pretty easy to tell the difference. 86-88 had black molding while 89-91 had a different body colored molding. The front ends were different as well. The front on the 89-91 was more aggressive and was finished with a lip while the 86-88 just slanted in. You would know what I am talking about if you saw it. There were also differences in the interior as well but those 2 things along with the taillights should be more then enough to tell the difference unless of course all of this stuff has been swapped.