Raul:
Do a search on here about body height, or something like that.
One thread deals with how to set your rear suspension height (ignore that one for now) but another talks a lot about getting the body to sit correctly on the sub-frame so that it's level all around. this includes removing some or all of the rivets along the rear frame (along the engine bay), jacking the body only up or down to get the door gaps lined up and everything level, and then using bolts and stop nuts to hold everything in place. We do one side at a time, and use a 4"X 4" beam under the rear corner of the body to jack it up and keep it level. It's an easy job, just time consuming.
Let me know if you can't find it and I'll search for it, too.
Gordon
(edit update) I poked around with a search on "door gap" and got some good info. Not the detailed one I was looking for, but a good start....