I thought this was pretty technically advanced in 1980. http://www.technicopedia.com/8860.html
I had the previous one: http://www.technicopedia.com/853.html - which didn't have a rear differential. My father (an engineer) made one from regular bits which was spun by a large pulley with (trigger warning!) the centre drilled out so an axle could freely pass through it.
It was also great when the electric motors and battery box came out. With a bit of gear work, you could actually take that 853 and motorize it... working engine and all.