There is really no 'original 5x5' in terms of a program. It is a concept, a training theory, "5x5" is a nice, simple way to package and present that theory in a way so that most people will not screw it up.
The concept has been around for God knows how long. Bill Starr and Tommy Suggs were heavily influenced by a lot of what Doug Hepburn was doing. Bill Pearl built world-class strength and a world-class physique with this concept. Starr and Suggs' felt that 4-6 sets of 4-6 reps was a good range that just about anybody could progress with, it is high enough reps that you're out of that neural range, and it is low enough to allow progression of strength. They concluded this from a lifetime of competing, training, and working with other athletes.
Starr figured that 4-6 sets of 4-6 reps was a little complicated, and people would probably screw it up, he and Suggs decided that 5x5 was nice, effective, simple, and just about impossible to screw up.
Originally, Starr's program built a base by training M-W-F or Tues-Thurs-Sat.....the Big 3 lifts were the Back Squat, Power Clean, and Flat Bench. Flat bench was in place of incline because many hig hschool gyms didn't have incline benches at the time, but Starr admitts that he feels inclines are a better choice for an athlete because of the shoulder recruitment.
Over the eyars people have personalized this. Those who do not need explosive strength and/or do not know how to clean correctly can deadlift or barbell row...you can OHP or Incline instead of Flat Bench, etc......
Basically, there is no "old 5x5".....it is a concept of progressively getting better at a squat, a back lift (pull), and an upper body press over a set number of sets/reps on set days so that you have a constant and workload is quantifiable, thus allowing a clear, measurable plan for progress.
The concept is so simple, it's beautiful, once you have good form and understand the concept, the only way to fuck it up is to overcomplicate, micromanage and overanalyze it.