According to a segment in one of Hatfield's books I have, this was actually 525 pounds, even though Youtube says 220 kilos and Irongame says it's 500 pounds. Awesome historic video regardless, from "The Great American Squat-Off". This was an exhibition where a world champion bodybuilder "The Golden Eagle" challenged world champion powerlifter "Dr. Squat" to a squatting contest. In maximum weight lifted, Platz got beat (600 pounds to Hatfield's 840; I believe these were "RAW" numbers). However, Dr Squat got his butt whipped when it came time for the the reps contest. Hatfield did 11 reps with the 525 pounds, while Platz did the 23 reps that we see in the video.
I'm thinking that the side spotter shown at the end is Lawrence Pfohl, aka professional wrestler "Lex Luger".