MTZ XXX

It's not a porno. XXX is just Roman numerals. In 1976 Minsk Tractor Works (MTZ) celebrated 30 years jubilee.

Letter index means "cotton". Special version for cotton plantations. Rear wheel drive and increased steering angle.
Base model with rear wheel drive.
Base model with all wheel drive.
Is based on 80 model (surprise) and is designed for use on steep slopes. Letter index means "lower road clearance".
Another advanced model for steep slopes. Leter index means "steep slopes". Really cool.
Letter index means "semi-caterpillar". I never seen it in real life.