I just got a 1985 Supra P-Type and I need to know the rear end gear ratio, ring gear diameter, and also if it's a LSD. I figured I'd ask on here before I took the rear end apart and tried to figure it out myself. Can anyone answer and save me this trouble???

Your car's original diff was an F283, which is a 4.30:1 LSD. If it's been changed, pull the rear cover off the diff and count the teeth OR spin the tailshaft one revolution and count the wheel revolutions.
Axle F283: F = 7.5" Ring Gear Diameter. 28 = 4.30 ratio.
Go to www.celicasupra.com
Their forum is more extremely informative for the MKII and everyone is very helpful if you run into any problems.

Thanks! That will save me a lot of trouble!

If your car is an auto it'll be a 4.11 LSD on the 5spd from 84+ were 4.30:1

1985 Super Silver Supra P-type 89k
slightly modded
2000 Toyota Solara TRD Stage 3 85k