I don't know years.. Still learning them. I hope I get this right otherwise I'm gona look like an idiot.
CJ5 - Round headlights. Built by AMC, no "trunk" seat sits right at the back. Door frame curves in.
CJ7 - AMC/Chrysler?? 10" trunk behind seats. YJ shaped doors. Round headlights.
CJ8 - a.k.a Scrambler. Not too many made. 10"? longer then a CJ7? Round headlights.
YJ - Two major versions. Pre and post 1991 Square headlights. Same length as CJ7. Pre 91, Carbed 4.2L and slanted rear rollcage. Post 91. Fuel injected 4.0 and rear "ears" for passanger safety.
TJ - Roundheadlights. Fuel injected 4.0 . Rear ears, same length as YJ/CJ7. Coil suspention not spring.
That's about it. I know I must have got some things wrong.
I got a '89 YJ and I am very pleased with it. It seems like alot of the CJ7 tech applies to the YJ, which is a bonus because there is alot of CJ7 tech and mods out there.
The 89 is simple enough to be worked on by someone who doesn't have a clue, at the same time as being new enough that not every component needs to be changed out.
I belive for a '79 you need to look for frame cracks behind the front spring hangers? as well as all the other things to look at when buying a car that's 22(nearly 23) years old.
Anything that looks jury rigged is bad. Swaps and rebuilds can go either way. On one had you think. "Wow, fresh rebuild, thats great." on the other hand you say "Well, just rebuilt, what was wrong with it."
All I can say about buying a Jeep is that mines only 12 years old and I'm constantly under it fixing stuff.
But it's all simple enough for me to fix.