Are all the fullfloater axle shafts the same? What I'm wondering is if the non locker axle shafts work with the locker? I seem to remember the answer is no because they don't have as long of splines. But, I just wanted to check.
The axles are the same diameter / spline pitch allowing interchangeability.
You are right about the spline length, which is needed for the elocker. Even with the lockers the opposing side axles are interchangeable with equal length splines
In the case of the FF 80 series rear axle there are 3 part numbers. Left and right side numbers are different and the RH has a lock and non-lock version.
In addition, there have been multiple supercessions on all three axles and the diameter of the shaft where the seal rides was increased from 35 to 36 mm. It is important to know what you have in there as the newer shaft requires a different oil seal.
The smaller shaft was the one used in production so if the shafts are original to the vehicle one would use the smaller seal. If the shafts are replacements, one needs to know what was used to obtain the proper seal.