The 84r will have smaller diameter forks, so they will bend easier, they have around 8 inches of travel front and rear VS 9.8 front and rear on the liquid r.
Power difference is huge. I have an 84 with DG pipe and silencer, boyesen reeds, UNI air filter with drilled air box. And it has ok power, but not compared to a liquid r.
The 84 has a 5 speed transmission.
In my opinion if there jetted right, and maintenance is done, and the motor is in decent shape, the air cooled motor will last a long time. Not as long as a liquid cooled 250r though.
Hope this helps.
1983 ATC 200x
1982 ATC 250R X2
1983 ATC 250R : Future build
1985 ATC 250R : Main rider
1985 ATC 363R Duner
1985 ATC 250R X2 : Future build
1986 ATC 250ES