Look up Carrier breaks for the D35. I think it's 3.54 & up. However I suggest & others will too that you put the Spartan in the front D30 with a carrier break of 3.73 up.

 

You're going to have to pull the carrier apart and measure the diameter of the pin.

 

I think you had two identical posts a while back that I answered on but I guess it got deleted. Those numbers are the carrier bore size. 1.56 is '94 and newer D35 and 1.625 is '94 and older D35. The 1994's depend on production date. Since you are in the TJ section i assume you are asking about a TJ therefore you will need the 1.56.

 

Put it in the D30 up front. An automatic locker in the rear can cause driving problems and may break the D35. Also, you already have an LSD in the rear. A locker up front would be an ideal combination.