Gathering parts for front disc brakes for 1969

[dmjlambert]

OK regarding Motive Gear MG6569 replacement axle shafts. I have measured the center hole of the 71 rear brake drum at 3-1/8 inch and found info in the Q&A on Summit’s site that says the brake pilot is 3.06" so that will fit.

The specs say the shaft is 30.5" long. Is there a way for me to confirm the length and that I'm getting the right one without taking the axle out of the differential? I see Motive Gear has another axle shaft part number 14071751 with length 31.281" long and 71 C10 is in the fitment list. So I suppose that is the longer of the two choices and the one I should not choose.

Should I drain the differential and remove the axle before I order? Or is there another way to verify I have the shorter differential of 1969? If I do remove the axle, where are the measurements taken from on the axle shaft?