5 lug axle?

[1moretoy]

i have a 70 1/2 ton short step. i know 70 was the year of two diffrent axle length's. anyone know what each one measures, i want to know wich one i have the longer or shorter. im going to convert to 5x5 and disc brakes. summit says they have axles made by superior for $100.00 ea. that measure 31.312 does this sound right? also what series carrier do theese 12 bolt's have. i want to run a 3.73 or 4.11 gear ratio. will i have to upgrade the carrier. sorry for the list of questions thanks