In '62, '63, & '64, the 2000 was essentially the 600/700 and the 4000 the 800/900 in a blue paint scheam. In '65 they changed to three cylinder engines, added the 3000 and 5000 to the line. TOTALLY different tractors.
In '68 there were some changes, most obvious was the grill. They were made thru '75.
My 3000 is my most used tractor! At aprox. 34 hp and 3400 lbs. it is a very useful utility tractor. Don't see many on the market as they seem to be in demand.