Yukon Axles

Bought a set of Yukon axles for my 71 Demon. Stock housing dimensions and the axles are 28 inches in length. I have the green bearings with 3 inch studs. When I bought the housing it had No axles and I was offered a 4:10 or 3:91 center section. I chose the 4:10 with the clutch type sure-grip. Put it all together and first time out tore the splines off one of the axles. It looks like the axle only went into the diff side gear carrier about 1/4 of an inch. Called the place where I bought the axles and they said that I had to remove the centering pin in the diff. Axles didn't go in any further. Do I need special length axles or are they different length between the cone type diff than the old clutch type. Has anybody ran across this before. I put the axles back in and parked the car for the winter. Didn't take any pics. Thinking of getting new ones soon.

Kenny B