'86-89 TRX and '86 ATC axles are interchangeable. I don't think there's any difference in the length. '85 ATC axle is different. I am currently using a 400EX axle in my '86 ATC, with 400EX hubs, 250R locknut, brake hub and rotor, 250R sprocket. 400EX sprocket may fit a little better, but the brake rotor on a 400EX is larger diameter and won't work. 400EX hubs do not fit on 250R axle.
[FONT="Palatino Linotype"]~My Rides (to name a few) ~
1986 ATC250R, 1985 ATC350X
1985 ATC250R Missile (90% done)
1983 ATC185S
1999 TRX416EX
2003 Honda CBR600RR
1990 Yamaha Zuma
1985 XR80 w/100 motor
1967 Honda CB77, '65 CL77
1962 Puch 250 SGS
1984 XR350R (owned since I was a kid)
1972 Suzuki T350 Rebel, '73 T500 Titan
1964 BSA A65 (needs restored)
1968 BMW R60/2 mint original bike
1976 Kawasaki KH500 triple
Anybody have parts to trade for the above models?