I think poorboy is on the right track with the c-clips

my lock right locker for the 9 1/4 has in the instructions that with the early sbp axles to use those c-clips and when going into the 85-up 9 1/4 use the c-clips and notes they are 2 different thickness.

myself, i would go a little further and maybe check the stock side gears/spiders to make sure they are the same or different to match the different c-clips.

would be good info to know if the c-clip change with axle is all thats needed... so far as long as I can remember it has been a no swap deal and all hear say...

man that would save a lot of work and $$$ when swaping wbp on the dodge trucks.

do the 8 1/4 axles inter-change axles from swb to lwb axles???

I have 2 of those 10 bolts so I guess a rainy day would let me find out.