84 & 85 are the same bike apart from tank stickers. 86 is the same except for the disc front.
They can have problems with cracking barrels, and plastics are hard to get. The motor is midrange focused - the KDX200 of the same age has a considerably better motor (and steers much better). The IT has better suspension, with more room for improvement.
The 1986 YZ250S is a good thing, and would be more than welcome in the Pre-90 class.
Big hit in the upper midrange makes them exciting to ride, apparently.
Pretty solid bikes. The same basic motor ran from 1983 to at least 1987, so parts are easy to come by.
The forks lacked the sophistication of the '86+ Honda cartridge forks, but aren't rubbish. Could be swapped to Honda or '88 YZ forks if you were really worried.
You can buy 87 plastics from UFO (same shape, just white radiator shrouds rather than the '86's red).