Built the first version and I had problems keeping things in snyc. Heard about the update, so I'm rebuilding it. Would find it helpful if length of axles was listed in the various steps in the instructions. Got to step 69 and not sure of the axle length. Are they 6L? Also, is there a particular reason you used 48496's instead of the 87408's in the original version or are they interchangeable?